Fuel Economy / Jack Plate? - www.ifish.net

Go Back   www.ifish.net > Ifish Fishing and Hunting > Boat and Motor Tech

Reply
 
Thread Tools Search this Thread Display Modes
Old 05-27-2006, 11:21 PM   #1
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Fuel Economy / Jack Plate?

I love my new boat, but it has a drinking problem. It is a 19'6" Duckworth with an 18-degree hull and a Merc 150 2-stroke on an offshore bracket. The motor is a '96 Black Max XRI (fuel and oil injected) with a custom 5-bladed stainless power prop (not sure of the pitch). I haven't exactly been light on the throttle, but I'm only getting about one mile per gallon (seriously, maybe one and a half, or 22-25 gph burn rate on plane). I only have a 38 gallon tank, and some of the fishing I want to do exceeds my range (I don't mean tuna, I just want to be able to safely run around nearshore in the ocean or be able to run up to Kelly Point if the fishing is slow in St Helens, etc).

I am planning to add a fuel flow meter to check optimum trim angle and rpm, as well as to determine which future modifications may help reduce fuel burn (I am planning to add a "whale tale" or "edge" hydrofoil, and also to try other prop pitches). I am open to any suggestions regarding fuel economy, but one specific question would be if a "jack plate" might make a noticeable difference. I moore the boat, so I haven't had it on the trailer since the day after I bought it, but I'm wondering if the motor might be hung too low (the motor is a long-shaft, and it is mounted on the offshore bracket which is well below the transom height). I don't know anything about jack plates except that they move the motor back slightly and allow you to adjust the height for optimum performance. I really don't want the motor further back, but I would do it if adjusting the height would make a significant difference. How far below the transom should the cavitation plate be? With the motor 2 1/2' back on the offshore bracket (bracket angles up from the transom rather than having a planing surface), does it need to be below the transom at all? Also, I noticed that the more expensive jack plates are hydraulically adjustable while the less expensive ones are adjusted by loosening or tightening adjusting bolts; is there a huge advantage to adjusting it on the fly, or could I go the cheaper route and just leave it once it's adjusted correctly?

__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 05-28-2006, 05:32 AM   #2
Starfish
Moderator
 
Join Date: Mar 2004
Location: Richland, WA
Posts: 5,810
Default Re: Fuel Economy / Jack Plate?

Wow! Mine drinks fuel like that but it's a 225hp Merc and I run it hard. I would have expected 15-17 gph with a 150. Anyway, improving your boat setup won't decrease the number of gallons per hour your motor will drink at WOT but it will sure increase your top speed, so the net effect will be more efficiency.

With the motor on an offshore bracket you ought to be able to raise the motor pretty high without needing a jackplate. (An additional setback probably would not be desirable if you're already 2.5' back from the transom.) As the motor gets farther and farther back from the transom it can be raised more and more-- that's why the bass boats use setback jackplates, to let them raise the motors and cut down on drag in the water. My boat (without a jackplate but with a pretty aggressive step pad built in) has the motor set with the main cav plate about 3" above the bottom of the hull, so the top of the prop is just about even with the hull. That's an extremely high setting and the boat shop was skeptical when I requested it, but as it turned out it works fine because of the hull design (pretty unique for an aluminum hull).

Here's a picture for comparison:


The High Five prop you're running is a very capable prop for running in elevated positions. You should try raising the motor as high as it will go in the existing mounting holes and see how the boat performs. If it still doesn't give you enough height you could try a manual jackplate with the least amount of setback you can find, probably 3 or 4 inches. Keep raising the motor until you lose your grip on turns, then back it down a notch. If you run in a lot of really rough water you should err on the low side. If you're raising it very high keep an eye on your telltale stream to make sure the motor is getting enough cooling water.

The other thing you ought to check is to make sure you're running the right pitch prop. Check your WOT RPM's against the manufacturer's recommendation and make sure you're at the high end of that range when the boat is lightly loaded. But don't swap props until you've raised the motor-- raising the motor will raise your RPMs (and top speed) unless you've raised it too far. You can also try different prop designs; the High Five is an awesome prop for hole shot and for holding in rough water, but it has almost no reverse thrust and isn't the fastest top end (although not bad at all). I like the Tempest Plus (3 blade) a lot, best top speed and really good all around performance. Some folks prefer four-blade props such as a Trophy or Rev 4 for rough water use.

Good luck, let us know how it works out!
Starfish is offline   Reply With Quote
Old 05-28-2006, 05:40 AM   #3
Starfish
Moderator
 
Join Date: Mar 2004
Location: Richland, WA
Posts: 5,810
Default Re: Fuel Economy / Jack Plate?

Oh, one other thing-- I noticed you plan on installing a hydrofoil. If you're having trouble with your hole shot or with keeping the bow down at low planing speeds that can help, but otherwise it won't help your efficiency and might hurt by adding a little more drag. Proper use of the trim switch, the right prop, and the right motor height would be the first things to try before installing a foil.
Starfish is offline   Reply With Quote
 
Old 05-28-2006, 10:47 PM   #4
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

Wow, thanks Starfish. I'll need to chew on your response for a while, but that's a lot of good info. You hit the nail on the head with your description of my prop characteristics (great hole-shot but no reverse thrust - I got myself in trouble the first time I needed reverse badly).

The reason I'm considering a hydrofoil is too get more positive feedback from my trim settings. My last two boats were Merc I/O 's with Stingray hydrofoils, and there was much more response from a touch of the trim button. On this boat, I can't really feel much difference between full-down and trimmed correctly, and I usually end up trimming too high and porpoising (I'm not sure if this has anything to do with the offshore bracket or if it is just due to the lack of a hydrofoil and the light bow). By the way, do you have any opinion between the "whale tail" and the "edge" foils?

As I mentioned, I haven't had the boat out of the water, so I can't picture how high the motor is, but your picture gives me something to compare to as the upper extreme. I may email you a pic of mine next time it's on the trailer for your opinion. Your description of the advantages of raising the motor make sense, but I'm a little nervous based on your statement that raising it too high could make it skid in turns. It already skids more than I'm used to in tight turns (not badly, just more than I'm used to). I was assuming that the skidding was due to the motor being so far back - putting the pivot point further from the boat and having the torque from the motor pushing it like a fulcrum.

I also may have more questions for you regarding the prop. I have the stock prop that I can try for comparison, and I have a Merc 4-bladed aluminum prop off my old boat if it will fit (I'll call the dealer before trying it).

I'll try not to bug you until I have more information. I need to install a tach and a fuel-flow sensor so that I have a starting point to compare any changes to (for some reason it was apparently ordered without a guage package - no tach, speedo, voltmeter or anything, just a stupid inaccurate fuel guage). Thanks again for your help, and I will be back in touch once I have more pertinent information. I love the boat, but I need to get it dialed in for my uses.
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 05-29-2006, 06:54 AM   #5
Okie
Tuna!
 
Join Date: Jun 2003
Location: Cedar Mill, Oregon
Posts: 1,462
Default Re: Fuel Economy / Jack Plate?

When you say you are geting only one mile per gallon, I believe this is incorrect. The only way to measure gas consumption on water is with a GPH meter. Gas per hour consusumed. This could be many miles or less depending on water conditions.

With the GPH meter you can see the correct RPM to operate at in order to get the best distance out of a gallon of gas.
Install a GPH meter on your boat for accurate readings.

Good Luck;
Okie is offline   Reply With Quote
Old 05-29-2006, 12:29 PM   #6
trap50
Ifish Nate
 
trap50's Avatar
 
Join Date: Oct 2002
Location: Salem
Posts: 2,388
Default Re: Fuel Economy / Jack Plate?

If you know how many gallons you burn and have a GPS why can't you take the total mile vers the total gallons just like a car?
__________________
trap50 is offline   Reply With Quote
Old 05-29-2006, 04:10 PM   #7
Draggin' Bait
Steelhead
 
Join Date: Sep 2004
Posts: 348
Default Re: Fuel Economy / Jack Plate?

Another item I'd recommend is pulling the boat from the water and checking to ensure you don't have some marine growth "anchors" below the water line. It doesn't take a lot of marine growth to really increase underwater friction. Can you raise you engine one or two holes on the transom? That would be way cheaper than a jackplate. I'd also second the thought that a 150 should not be drinking that fast at WOT -- 15-17 gph would be about max, I'd think. Boat Doc would know.
Draggin' Bait is offline   Reply With Quote
Old 05-29-2006, 09:39 PM   #8
Starfish
Moderator
 
Join Date: Mar 2004
Location: Richland, WA
Posts: 5,810
Default Re: Fuel Economy / Jack Plate?

I'd definitely get a tach right away before making any adjustments-- it's super important for the health of your motor to make sure you're running in the right RPM range. It'll also help you dial in the most efficient setup.

When I talked about losing your grip in turns, I didn't mean the whole boat would slide-- rather that the motor will ventilate and the prop will lose its grip while powering through a turn (you'll hear the motor rev suddenly) if it's set up too high. Same thing in rough water.

I don't have much experience with hydrofoils on larger boats so I can't make a recommendation. I did have a buddy with an I/O runabout and addition of a hydrofoil made a huge improvement in hole shot for skiing, but it doesn't sound like you're having trouble with holeshot. Trying to get more response from your trim setting can just as likely be fixed with prop selection or motor height, so I wouldn't rush into getting the foil until you've eliminated other factors.

Let us know what pitches your props are, especially the High Five, and when you get a tach so you can know your WOT RPMs you'll know a lot more about prop options.

One last caution-- don't assume too much expertise on my part! I'm just a fisherman with a need for speed, so I've done a little homework looking into performance issues on my own boats and have set up and helped tune a few of my friends. I'm not a professional... my advice is freely given and worth every penny!
Starfish is offline   Reply With Quote
Old 05-29-2006, 09:55 PM   #9
Flatfish
King Salmon
 
Join Date: Dec 2001
Location: Mulletville
Posts: 12,511
Default Re: Fuel Economy / Jack Plate?

Back off the gas when on step.

My plate does more good with a pump mileage wise than with the prop. Not enough difference to justify itself in a prop only situation.

Call Stevens about the prop pitch. They should be able to point you in a good direction.

Mark and the dog
__________________
A curious thing happens when hatchery fish stocks decline: People who aren't aware of the old levels accept the new ones as normal. Over generations, societies adjust their expectations downward to match prevailing conditions
Flatfish is offline   Reply With Quote
Old 05-29-2006, 10:27 PM   #10
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

Thanks DB. It has some growth, but not a lot yet. It has been in the water since I bought it in March, but the growth seems to get worse once the water warms. I have to pull it out of the water to do my 10hr. maintenance to the new kicker, so I'll look to see if I can move the motor up using the existing mounts.
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 05-29-2006, 10:39 PM   #11
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

"Back off the gas when on step."

What did he say, Dear? He said he thinks he knows you! :smile:

Starfish, thanks again for the input. I'll have to see if I can feel it losing it's grip; I've mostly just heard it. I'll let you know when I see what pitch the prop is. Also, thanks for the disclaimer; I didn't mean to assume that you are an expert, but you obviously have more knowledge than I do.
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 05-30-2006, 02:43 PM   #12
Chrome Bumper
King Salmon
 
Chrome Bumper's Avatar
 
Join Date: Apr 2002
Location: Redd
Posts: 9,914
Default Re: Fuel Economy / Jack Plate?

Your cavitation plate should be a inch above the keel for each foot of setback. Use a straight edge off the keel With a vee hull you can go just a bit higher.

You may be able to move the motor up a couple of bolt holes with out making more. Bass boats use jackplates to lift the motor higher for speed, just the bottom of the prop contacting the water, but you get cavitation and you can 'blow out' at speed, which is a quick uncontrolled 180 type manuever. Also low water cooling water pickups may be required.

Fewer blade are more efficient, but one bladed props are kinda rough. I would recommend a 3 bladed aluminum spare prop as a spare. Something around a 19 inch pitch, go with a slightly larger than stock diameter if you want optimum cruising efficiency. Aluminum tends to break before your lower end when you hit some of that stuff in the water. Stainless blades are thinnner, so more efficient than aluminum.

The prop shop east of Oregon City will let you try their reconditioned props before you buy.

Is the bottom of your boat clean(them weeds slow ya down big time.) and is the bottom flat? a hooked hull suck gas too.

If you aren't chaseing bass (just how fast are those fish anyway?) you just need to get it adjusted once.

Having your motor 'to low' is good if you need to manuever at low speed in current and swell, like if you are surveying the jetties or some such.

You can break your cavitation plate with those wings if you are not careful.

What's a custom prop?? Don't prop manufacturers know what they are doing? Seem's like an outfit like Michigan wheel could build a prop after practicing a hundred years.

Does your weight distribution (your boat's) cause good trim? If not maybe trim tabs are in order or move cargo around.

Jack plates will increase you setback even more. Maybe (probably) you don't want that.

I think I saw some used 4 strokes in the classified ads, if you can slide that by your finacial officer that will give you better range.

Is your engine well tuned and not been modified, say with larger gas jets?

If you look where your motor is bolted on you will see that there are several holes to allow you to adjust the motor's running heigth, start there.

You should be around 2.5-3 mpg on flat water at 2/3 throttle it seems like.

Do you have a tach to check your WOT RPM?

Now you know why you see me buzzing around in the channel in my itty bitty 15gpm boat instead of one of my bigger ones.
__________________
Tight lines
Chrome Bumper is offline   Reply With Quote
Old 05-31-2006, 08:57 AM   #13
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

"You can break your cavitation plate with those wings if you are not careful."

That's why I was looking at the two models I mentioned. Apparently they both attach below the cav plate rather than on top, which supposedly reduces the chance of breaking the plate.


"Does your weight distribution (your boat's) cause good trim? If not maybe trim tabs are in order or move cargo around."

Boat seems very heavy in the stern. I don't know how to lighten the stern, so I was going to try adding weight to the bow.


"Is your engine well tuned and not been modified, say with larger gas jets?"

Good question. I was told the original owner liked to go fast, so I'll have to ask him if he re-jetted it.


"I think I saw some used 4 strokes in the classified ads, if you can slide that by your finacial officer that will give you better range."

If I don't figure out how to get the current configuration more efficient, then a 4-stroke will pay for itself.
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 06-01-2006, 10:26 AM   #14
Lund
Tuna!
 
Join Date: Sep 2001
Location: water
Posts: 1,511
Default Re: Fuel Economy / Jack Plate?

I run a prop year round. One thing I have noticed is with the larger pitched props, you will burn more fuel. With a boat of your size and hp, I'd be running a 15-17 pitch at the most. The heavier the boat the smaller pitch. If you were running a bass boat then go to the 21+ pitch. Not knowing what you're running on your boat, but looking at the picture, i'd bet you're running a 20 or better.
Lund is offline   Reply With Quote
Old 06-01-2006, 11:51 AM   #15
BrionLutz
Ifish Nate
 
Join Date: Jan 2003
Location: Portland, OR
Posts: 2,425
Default Re: Fuel Economy / Jack Plate?

Hmmm...at 1mpg with new boat and motor, you either have a serious problem or your calcs need some fine tuning.

Here's the Yamaha Performance Bulletin for a 19' Duckworth with a 150HP 4 stroke. 6.26mpg at 21mph is best. The worst is WOT at 3.16mpg. Two strokes use a bit more fuel but not 3 times the amount of fuel of a 4 stroke.

You probably need to check your calcs first. Something is way off.

Yamaha Performance Bulletin 150HP/Duckworkth 19' Advantage.
BrionLutz is offline   Reply With Quote
Old 06-01-2006, 02:36 PM   #16
Okie
Tuna!
 
Join Date: Jun 2003
Location: Cedar Mill, Oregon
Posts: 1,462
Default Re: Fuel Economy / Jack Plate?

Look at "Floscan" GPH meters for accurate gas consumption readings.

http://www.floscan.com/html/blue/recreationalmarine.php

Good Luck
Okie is offline   Reply With Quote
Old 06-01-2006, 04:44 PM   #17
BrionLutz
Ifish Nate
 
Join Date: Jan 2003
Location: Portland, OR
Posts: 2,425
Default Re: Fuel Economy / Jack Plate?

I already have a FloScan but I'm not sure the FloScan would work on the older 96 Merc that Beefcake has...and they are expensive...mine was $800 not counting installation.

Something is really wrong with the original 1mpg estimate...the motor would have to be dumping fuel out the exhaust (which is possible if the engine is shot) or he's got the anchor out or something.

First thing is to figure out what is the real current mpg.
BrionLutz is offline   Reply With Quote
Old 06-01-2006, 04:55 PM   #18
Tinman
 
Join Date: Aug 2000
Location: Portland & Oceanside, Oregon
Posts: 8,756
Default Re: Fuel Economy / Jack Plate?

Rule of thumb says max WOT fuel consumption is hp divided by 10. In other words, your 150 should burn 15 gallons per hour at wide open throttle. At cruising speeds you should burn 8 gph. I suspect you have two problems. First, you are seriously stern heavy. Try temporarily taking 300 pounds out of the stern (gear, extra batteries, extra fuel, etc.) and see if things improve. Second, you may have the wrong prop pitch. The only way to check that is with a tach.
__________________
...become the captain everyone respects... https://www.theoceancoach.com/
Tinman is offline   Reply With Quote
Old 06-01-2006, 05:04 PM   #19
Okie
Tuna!
 
Join Date: Jun 2003
Location: Cedar Mill, Oregon
Posts: 1,462
Default Re: Fuel Economy / Jack Plate?

If you paid $800 dollars for a Floscan meter you are way above the normal cost.

You can check the going price on the internet for your engine.
Okie is offline   Reply With Quote
Old 06-01-2006, 08:46 PM   #20
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

Thanks everyone. I will update once I have more info. After re-thinking everything, I think I made two wrong conclusions. First, I think I was a little heavier on the throttle than I gave myself credit for. I went for a ride today, and learned that the boat handles fine at 27-30 mph instead of 40+ like I had been running it; I just don't get there as fast. Second, I may have been off on my mpg, but not by as much as you might guess. I think I wen't further than I thought, averaging 75-90% throttle, so now I'm thinking I was actually getting about 1.5-1.9 mpg. Heck, if I back off to 2/3 throttle, maybe I can break 3 mpg.

I will be adding a tach and a fuel flow meter, so I guess we shouldn't speculate further until I have hard data. Thanks again for all of the input so far. I will be looking for more advice once I have the facts. I'd love to be able to run out for halibut someday (with enough fuel to return).
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 06-01-2006, 10:37 PM   #21
BrionLutz
Ifish Nate
 
Join Date: Jan 2003
Location: Portland, OR
Posts: 2,425
Default Re: Fuel Economy / Jack Plate?

"...now I'm thinking I was actually getting about 1.5-1.9 mpg. Heck, if I back off to 2/3 throttle, maybe I can break 3 mpg."

Those numbers make more sense for a light, flat bottomed, open boat running a jet outboard...and are as good as you'll get...especially for an older engine.
BrionLutz is offline   Reply With Quote
Old 06-01-2006, 10:58 PM   #22
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

I'm confused; it's not light, flat bottomed, open or a jet. It's a heavy, 18 degree v-hull, windshield boat with a prop.

Maybe I'm just used to the economy of the 120 Mercruiser I/O's in my last two boats. You mean it's gonna cost me more to have a faster boat? :smile: My last trip in my old boat (19' Bayliner), I ran pretty much wide open for 4-5 hours and it cost me about $75 in gas. In my new boat, I can burn $100 in two hours. Ouch! Sir, step away from the throttle...

Oh well, I bought a couple of spare portable 6 gallon gas tanks last week to extend my range slightly. Maybe I need a couple more.
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 06-02-2006, 10:23 AM   #23
Chrome Bumper
King Salmon
 
Chrome Bumper's Avatar
 
Join Date: Apr 2002
Location: Redd
Posts: 9,914
Default Re: Fuel Economy / Jack Plate?

Trim tabs will give you a cadillac ride and allow you to plane slower and ajust for load and seastate. A fairly slow plane is where you should get your highest range. (Unless you want to move slower than the hull speed, like 8 MPH (7 kt).)

A 150 will burn $50 an hour WOT. Welcome to the world of two strokes.

You should be able to plane easy at around 3600 RPM, use the steepest pitch 3 blade prop your motor will push without lugging/straining. Keep that purty 5 blade thing for when you want to get squirrely, or break the 3 blade.

The prop shop east of OC will let you test drive reconditioned props.

One size bigger dia. than stock may help effieciency at mid-lower RPM.

Quit pushing the throttle to the stop and leaving it there!
__________________
Tight lines
Chrome Bumper is offline   Reply With Quote
Old 06-10-2006, 01:56 PM   #24
slowbuilder2005
Chromer
 
slowbuilder2005's Avatar
 
Join Date: Apr 2003
Location: North Albany, OR
Posts: 606
Default Re: Fuel Economy / Jack Plate?

Quote:
Hmmm...at 1mpg with new boat and motor, you either have a serious problem or your calcs need some fine tuning.

Here's the Yamaha Performance Bulletin for a 19' Duckworth with a 150HP 4 stroke. 6.26mpg at 21mph is best. The worst is WOT at 3.16mpg. Two strokes use a bit more fuel but not 3 times the amount of fuel of a 4 stroke.

You probably need to check your calcs first. Something is way off.

Yamaha Performance Bulletin 150HP/Duckworkth 19' Advantage.
It's not unusual for 200+ hp outboard boats to get less than 2 mpg (check with a 2-way run and a GPS), and it's not unusual for 150- hp outboards to get from 3 to 6 mpg. The factors involved include #1, the weight of the boat (as loaded), #2, the efficiency of the hull form (low deadrise is better, continuously changing deadrise from stern forward is less efficient, etc), and #3, the efficiency of the motor type and installation. It used to be that an inboard or stern drive would deliver the best mileage, although it's hard to tell because many high horsepower ones are running around and the story is not obvious. Outboards have come a long way but must be mounted properly (minimum drag) and trimmed correctly as well.

Friends of mine that have installed hydraulic jack plates and done efficiency checks with their FloScan systems find that the jack plate does NOT help a lot, but is wonderful for backing off a sandbar since your motor stays vertical as you raise it up.

A Navman or FloScan is the only way to check how well the boat and motor are trimmed out and for comparing 'improvements' along the way to see if you are getting improved efficiency or not. Sometimes the best efficiency can be found by adjusting both trim tabs and motor trim ...this is much better than using a hydrofoil (only 'right' at one speed and loses efficiency at all others). Prop selection for efficiency is important as well ...in general, 4-strokers get better efficiency at lower rpms (even if you have to oversize the motor a little to make it work) while 2-stroke motors need to 'discover' the best rpm that optimizes the trade-off between the rpm that gives highest torque and that which gives best efficiency. Again, that Navman or FloScan will be a big help here.

Good luck ...trying to get best mileage is a fun experiment. There's a guy named Sal Dimarco (sp?) in the forums at the Coastside Fishing Club ( http://www.coastsidefishingclub.com ) who's a real expert at these things and worth talking to. Lots of other good fishing info (especially tuna) at this site as well.

Have fun,

Brian
__________________
http://www.glacierboats.com/tongass

Psa 107:23-24 Those who go down to the sea in ships, Who do business on great waters; They have seen the works of the LORD, And His wonders in the deep.
slowbuilder2005 is offline   Reply With Quote
Old 06-11-2006, 09:07 AM   #25
Chesapeake
King Salmon
 
Join Date: Aug 2005
Location: Washougal, WA
Posts: 5,219
Default Re: Fuel Economy / Jack Plate?

I would suggest starting with the prop. To be getting 40+ MPH out of a 150 on a 19' welded V hull boat would suggest too much prop to me. I would think your WOT top speed with light load should be in the 38-40 MPH range with that setup. I would think a 3 blade 18 or 19 pitch would be about right. Traveling speed should be about 3/4 throttle and 30 mph.

Fuel consumption isnt going to be great but should be twice as good as you are reporting.

Just my
__________________
Rick Lee

"I'd have shot a bigger one, if he had shown himself first."
Deck boss on "J4".
Chesapeake is offline   Reply With Quote
Old 06-11-2006, 04:29 PM   #26
Chrome Bumper
King Salmon
 
Chrome Bumper's Avatar
 
Join Date: Apr 2002
Location: Redd
Posts: 9,914
Default Re: Fuel Economy / Jack Plate?

Nice post slowbuilder 2005!

2 stokes have a sweet spot in thier load/RPM range, you need a prop and engine position that makes best use of that. IE engine operating at max speed(mph) while in its sweet spot. Like 2/3 throttle, 30 mph, 3600-4000 rpm.

You can do it by feel, but a flowscan makes it easier. Any gear you can jettison?, Empty bottles, Jimmy Hoffa, anything?
__________________
Tight lines
Chrome Bumper is offline   Reply With Quote
Old 06-12-2006, 01:30 PM   #27
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

Thanks again SlowBldr, Chessie, and CB. I was going to let this thread die until I get the tach and flow meter installed, but you have given me more to think about.

One thing that stands out is that most of you are against using a hydrofoil. I have had them on 3 or 4 previous boats, and always liked the responsiveness to trim (I understand that trim tabs are the best solution, but I consider that overkill on a boat this size). I understand that they can cause the cav plate to break, so I am intending to get one of the two brands that installs below the cav plate, thereby spreading the torque and having less chance of breaking. My two main uses for the big motor are driving on plane to a spot to anchor & fish, and pulling the kids on a wakeboard. It seems that the foil will help me to plane quicker (especially if I switch to 3-blade prop), help me to set and hold the best trim angle, and help me to hold on plane at a lower speed. What are the downsides? Also, would a flat plate like "the Edge" have less or more drag than a "whale tail" (I think the whale tail is slightly curved with ribs on the underside, but sometimes a flat surface creates more drag than one that breaks the flow slighly)?
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 06-12-2006, 09:19 PM   #28
slowbuilder2005
Chromer
 
slowbuilder2005's Avatar
 
Join Date: Apr 2003
Location: North Albany, OR
Posts: 606
Default Re: Fuel Economy / Jack Plate?

Hydrofoils like the Doel-Fin (or Stingray) are designed to get you out of the hole faster, but others like the SE Sport lean towards controlling vertical motion of the bow at the top end (in addition to helping with cavitation and a bit on the hole shot). The Doel-Fin type will take some knots off the top end, but the other type 'may' add a few (depends on whether your boat needs the control or not.) Trim tabs won't help out of the hole but they do allow you to adjust boat trim fairly independently of the motor trim. This means that you can find both, the most efficient boat trim AND the most efficient motor trim. Takes a little (fun) experimenting, but once you know the answer then you know it. You save from then on. Also, note that your comment "overkill for a boat of this size" is somewhat of a misnomer. What a lot of people don't realize is how smaller and lighter boats can benefit from trim tabs... when it comes to ride comfort and efficiency, they can use it more than the heavies. The heavies may need it for other reasons, e.g. motor trim isn't enough or results in excessive trim, or to control porpoising etcetera.

I think you need to define your priorities. Follow the 90% rule. If 90% of your use is for sporty stuff like water skiing, hot rodding on lakes and the like, then hole shot may be what you want regardless of gas mileage or top end speed. If cruising to the rock pile while burning minimum gas is your primary use, then maybe the hydrofoil needs to go (and maybe the prop) and trim tabs may need to be put on. If maximum top-end speed is the goal, then the Stingray type hydrofoil, or NOTHING on the motor or stern, or maybe trim tabs may get you dialed in. Maybe lightening up the boat and/or changing your storage options around so you redistribute weight more effectively is the answer. You can usually go by at-rest trim on that last one BTW. Your boat should trim level or slightly up at the bow when sitting at the dock, e.g. not more than an inch higher at the bow than the stern. You can measure trim at rest by using a SmartLevel (reports out-of-level in degrees) and trig. If your waterline is around 20' and the boat is trimming 0.5 degrees (bow up), then the bow is trimming up by about 2 inches, e.g. 12*22*sin(0.5)

Have fun,
Brian
__________________
http://www.glacierboats.com/tongass

Psa 107:23-24 Those who go down to the sea in ships, Who do business on great waters; They have seen the works of the LORD, And His wonders in the deep.
slowbuilder2005 is offline   Reply With Quote
Old 06-13-2006, 06:46 AM   #29
Beefcake
Sturgeon
 
Beefcake's Avatar
 
Join Date: Aug 2003
Location: Clackamas, OR
Posts: 4,688
Default Re: Fuel Economy / Jack Plate?

Thanks Brian. I'll have to take a measurement, but I know I sit "bow-high" by quite a bit (3-4") at the dock. With the fuel tank in the back and the motors hanging 2 1/2' behind the boat (since the bracket isn't a planing surface, it acts like a lever), I think my only option to level it would be to add weight to the bow. I have mixed feelings about doing this. I'm hoping it will increase efficiency, and it should also increase my freeboard at the back corners, but it might cause problems if I take water over the bow or if I come over the backside of a wave too fast. The only option I've come up with is to plumb water from my livewell into the fish box in the bow, then fill the box with water for all uses other than ocean fishing.

Do any of you happen to have a good link to something I can read to learn about propellors? I can't seem to get the relationships between diameter, pitch, and number of blades through my head. I don't mind experimenting, but I need to know what I'm looking for. For instance, the stock prop on this motor was a 13" 3-blade 21-pitch; I don't know what the 5-blade stainless prop is that is currently installed; but I have a factory Merc aluminum 4-blade 14" 20-pitch prop that I can try, but I'd like to know ahead of time what to expect. For instance, if the replacement prop requires less torque to rotate than the stock one, will my motor over-rev and be in danger of failure?
__________________
F/V Super Cub
(Previously Yoda's MegaDory)
Beefcake is offline   Reply With Quote
Old 06-13-2006, 09:43 AM   #30
BrionLutz
Ifish Nate
 
Join Date: Jan 2003
Location: Portland, OR
Posts: 2,425
Default Re: Fuel Economy / Jack Plate?

"I'm confused; it's not light, flat bottomed, open or a jet. It's a heavy, 18 degree v-hull, windshield boat with a prop."

Then you are truly doing badly as the Yamaha Performance Bulletin on the Duckworth 19 shows 6mpg with a 150 4 stroke engine.

Your problem is probably just an older technology engine and it's worn out.
BrionLutz is offline   Reply With Quote
Old 06-13-2006, 09:52 AM   #31
BrionLutz
Ifish Nate
 
Join Date: Jan 2003
Location: Portland, OR
Posts: 2,425
Default Re: Fuel Economy / Jack Plate?

"It's not unusual for 200+ hp outboard boats to get less than 2 mpg"

Or less depending on the weight and design of the boat but I'm not sure that has much to do with a 19' boat with a 150 on it.

Fuel consumption is mostly tied to the weight of the boat with smaller variations for degree of v to the bottom.

Beefcake's boat per the Yamaha Performance Bulletin should be around 6mpg with a 4cycle so 4mpg with an older 2cycle is probably reasonable. His 3mpg is probably just the engine getting tired out.

His best use of dollars would be getting it tuned up and some compression readings to see what shape it's in. 3mpg with tired 2cycle is probably about right.
BrionLutz is offline   Reply With Quote
Old 06-13-2006, 10:49 AM   #32
slowbuilder2005
Chromer
 
slowbuilder2005's Avatar
 
Join Date: Apr 2003
Location: North Albany, OR
Posts: 606
Default Re: Fuel Economy / Jack Plate?


You can play around with propeller parameters here:

http://www.rbbi.com/folders/prop/propcalc.htm

And the "Propeller Handbook" by Dave Gerr is a good reference as well ...and so are the tech support folks at the various prop companies. The folks at Piranha were especially helpful ...while I'm an advocate of stiff shiny stainless props myself, the FRP prop that Piranha sells is pretty good. You can replace individual blades (or all of them) very easily while on the water and the Piranha people will let you try several pitches/diameters until you achieve the kind of performance that you're looking for.

Brian
__________________
http://www.glacierboats.com/tongass

Psa 107:23-24 Those who go down to the sea in ships, Who do business on great waters; They have seen the works of the LORD, And His wonders in the deep.
slowbuilder2005 is offline   Reply With Quote
Old 06-13-2006, 10:55 AM   #33
slowbuilder2005
Chromer
 
slowbuilder2005's Avatar
 
Join Date: Apr 2003
Location: North Albany, OR
Posts: 606
Default Re: Fuel Economy / Jack Plate?

Quote:
"It's not unusual for 200+ hp outboard boats to get less than 2 mpg"

Or less depending on the weight and design of the boat but I'm not sure that has much to do with a 19' boat with a 150 on it.

Fuel consumption is mostly tied to the weight of the boat with smaller variations for degree of v to the bottom.

Beefcake's boat per the Yamaha Performance Bulletin should be around 6mpg with a 4cycle so 4mpg with an older 2cycle is probably reasonable. His 3mpg is probably just the engine getting tired out.

His best use of dollars would be getting it tuned up and some compression readings to see what shape it's in. 3mpg with tired 2cycle is probably about right.
You make a very good point that his motor may well have issues and should be looked at closely. But note that his original post said "but I'm only getting about one mile per gallon", not 3 mpg. Something's funky... or several smaller 'somethings' all adding up.

Beefcake ...what color is your exhaust? A hint of blue is OK, but if you're getting lots of white, gray, or black exhaust (and if your exhaust 'port' is sooty) then it could be that your motor is running too rich. How do the plugs look? Black and sooty probably indicates the motor's running too rich as well. I don't know why we all got off on efficiency tangents without first considering the motor and motor condition itself ...my bad :smile:

Brian
__________________
http://www.glacierboats.com/tongass

Psa 107:23-24 Those who go down to the sea in ships, Who do business on great waters; They have seen the works of the LORD, And His wonders in the deep.
slowbuilder2005 is offline   Reply With Quote
Old 06-13-2006, 11:26 AM   #34
BrionLutz
Ifish Nate
 
Join Date: Jan 2003
Location: Portland, OR
Posts: 2,425
Default Re: Fuel Economy / Jack Plate?

"original post said "but I'm only getting about one mile per gallon", not 3 mpg"

I think Beefcake figured out that was wrong (1mpg has the anchor out or other major snafu) and his actual cruise was around 3mpg.

I'd start with the engine. If it's tuned up and good compression ratio, then next check RPM's at wide open throttle. If he's underpropped his RPM will be high, if he's overpropped, he'll be lower than the motors top end rating.

I'm not sure he was/is getting an accurate fuel consumption rate. It's hard to do without a real time, calibrated fuel flow meter tied into the GPS (what Yamaha uses for it's tests).

If engine's tuned and in good shape and his prop's right, he's probably as good as it gets on mileage.
BrionLutz is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Cast to



All times are GMT -8. The time now is 07:27 AM.

Terms of Service
 
Page generated in 1.25719 seconds with 54 queries