What is Porpoising?

Killertraylor · 03-12-2001, 08:28 PM

I've seen several posts in the North River Boat topic which refer to "Porpoising" I've never heard this term used to describe how a boat drives. What does it mean?

Pete · 03-12-2001, 08:54 PM

Porpoising is when a boat doesn't trim properly. If there is too much or too little lift a boat doesn't run flat. Instead, the boat kind of bounces, alternating between diving and lifting as it compensates for the trim problem.

MPT · 03-12-2001, 08:56 PM

What happens during porpoising is that your boat is usually traveling at a high rate of speed and it is trimmed where your bow is up in the air too high and so the outdrive pushes the boat upward like it is trying to climb out of the water like a dolphin swims through the surface of the water. Adjusting your trim down just below this porpoising affect should be your optimum setting for your boat to be planing at. This would also give you the fastest speed of your craft. I'm not sure if Jets have this problem but I know it is common for I.O.'s and outboards with props! Just be careful not to trim your outdrive too low or you will lose speed because your bow will be pushing the water instead of gliding over the top of it.

Killertraylor · 03-13-2001, 09:37 AM

Thanks, guys. I saw the term used frequently when people referred to North River boats. My 22' NR with 250 Yamaha Salwater Series and stainless prop doesn't do this at all - I do seem to remember a friend's 22' Weldcraft with inboard jet doing it, although it was so slight that it didn't seem to be bothersome.

Backlash2 · 03-13-2001, 09:43 AM

"Porpoising" is when a gal stands bent over against a chair with her legs.....ah, nevermind

Pete · 03-13-2001, 01:14 PM

The dreaded SportJet has an integral trim tab. I recall RT talking about the value of tabs on shorter sleds, but I don't think he was talking about inboards or controlling porpoising, but there's no reason one wouldn't consider it to improve performance.

new boat · 03-13-2001, 02:41 PM

Purchased a 23' Thunderjet Maxim in Jnauary, with the Marine Powere 454 Chevy and a Hamilton 212 Pump. Until I had the recommended number of hours on the engine for break-in, I did not run the boat at full throttle. At full throttle, the boat would porpoise. After speaking with Thunderjet, I bent the bottom extension downward approximately 1/8th of an inch, for three inchs each side of the keel line. Boat runs perfect now. Thunderjet says the boat was trimmed when if left the factory, but I added a 10 hp Honda kicker and the extra weight took the boat out of trim.

[This message has been edited by Proud TJ Driver (edited 03-13-2001).]

boater · 03-13-2001, 02:50 PM

up in alsaka most of the guides have trim tabs, they need them to plane the boat when they put about 4 55 gallon drums of fuel in it for a long trip.

Bait O' Eggs · 03-13-2001, 02:52 PM

Proud TJ - you wanna buy a bridge?

I have a hard time believing a 10 hp trolling motor threw your boat out of trim alignment. What are you gonna do when you have to haul a fish back to the dock, or take a buddy fishing, more bending? 100 pounds give or take screwing up the trim seems funny to me. I dont doubt it runs better now, since you say so. But I would be having a long talk with TJ about that before I got on that turnip wagon.

Finn-icky · 03-13-2001, 11:00 PM

Have any of you out there in ifish land ever hear of anyone needing to put trim tabs on a inboard sled with a pump?

Finn-icky · 03-14-2001, 03:24 AM

Two weeks ago I would have been with you Bait O' Eggs, but I was having a similar problem with my 23' Jetcraft. Jetcraft also blamed my 15HP 4 stroke kicker for changing the design criteria. I haven't bent my tabs yet, and probably won't. The idea makes me a bit nervous. Will probably do the hydralic tabs some time. I had the bottom strakes extended farther forward and that helped, but when I'm full on fuel (70 gals) it changes things again. They also claim that if the pinger for the electronics isn't mounted right it can change things. The jury is still out on that one. I believe it would have to protrude well below the bottom of the boat to make a difference.

Salmonator · 03-14-2001, 08:42 AM

I'm guessing PTJD's boat is porpoising only when empty or slightly loaded. The Maxim is a big boat and the motor and pump is for big load carrying. If the boat was trimmed to run perfectly while empty then it seems to me that when you loaded it down it would be pushing water. So I guess my point is that unless you have power tabs, you really can't have it trimmed perfectly at all load situations. I think i'd rather have a slight porpoise empty and run effecient loaded. Make sense?? Joe

Pilar · 03-14-2001, 09:00 AM

Apples and Oranges here but...........

My fiberglass boat needs a different trim setting every time I go out. The load out of gear, people and fuel is different every time. I use the GPS S.O.G. (Speed on ground) and set the trim by moving the outdrive up or down. Max speed for rpm is the right trim. Trim tabs are cool but hydraulic ones are expensive. Still it seems like the only option for a jet boat.

The bend is your friend!

boater · 03-14-2001, 03:19 PM

hey bait-o-eggs, to late, he already bought a bridge

boater · 03-14-2001, 05:31 PM

wave walking is common in boats with improperly designed lifting strakes, they work fine in fast water but if you get in alittle chop the bow will try to grab a wave and walk or bounce to the next wave from side to side , ive been in a few brand "X" boats that did this, it is a weird feeling.

03-15-2001, 06:53 AM

Again, the lack of basic knowledge from boat owners who have replied to this post is amazing. Perhaps you all did realize, but neglected to mention, that the main causes of porpoising are from improper trim and uneven weight distribution. Weight piled in the stern will caused the nose to lift, which at high speed will bounce or "porpoise". Improper "trim", or the attitude of the vessel, will also cause the bow to bounce.
If you experience porpoising more than likely there is too much weight to the rear of your boat. Try redistributing your gear forward to alleviate this problem. If the bouncing does not go away, you will need to re-trim the boat. If you have an outboard, stern drive, or a boat equipped with trim tabs, you can simply trim the nose down to correct the bounce. If you have a jet boat without trim tabs, you have a couple of options. Most jet boats in the industry have an extension of the bottom which protrudes below the transom, enabling you to bend the bottom plate up or down. Bending this plate down just an eighth inch will cause a large difference in the attitude of the boat. If this does not correct the problem the are wedges available for jet pumps which can be installed to redirect the angle of the jet nozzle. AT also has a turbine trim, or "jetivator", which will correct porpoising. If anyone else knows of an effective way to correct porpoising in a jet boat, hopefully they will post it here as well.
Anyone who owns a boat has already bought a bridge which can cross any waters.

03-15-2001, 06:58 AM

OK, maybe you guys did mention that stuff. It's just irritating to hear folks talk trash sometimes.

willierower · 03-15-2001, 07:17 AM

The trim solution for a je boat is called a Place Diverter. It adjusts the angle of the nozzle.

boater · 03-15-2001, 07:45 PM

this is a problem a new boat owner should check before he buys a new boat, not all the new sleds do this, so check around and talk to sled owners of as many brands as you can, this is a problem that should not happen in a new boat. just my 2 cents worth.
[This message has been edited by boater (edited 03-16-2001).]

[This message has been edited by boater (edited 03-16-2001).]

boater · 03-16-2001, 08:33 PM

jetstud, the way to correct this problem is build the boat correctly so customers dont have this problem . trim tabs ? porpose when empty but not full ? full tank of fuel changes boat attitude ? a 100 pound honda kicker makes it porpose ? what about a cooler with 100 pounds of fish, what about 3 other fisherman ? i am glad i bought a boat that doesnt have problems like this, you better look in the mirror when you say basic lack of knowledge, because this kind of problem should never reach the consumer on a new 40 plus thousand dollar boat.

Wood Shampoo · 03-16-2001, 08:43 PM

Boater-
What brand of boat might that be that you speak so highly of?

boater · 03-16-2001, 08:46 PM

one of those real ugly wooldridges.

Salmonator · 03-16-2001, 08:51 PM

Boater, have you ever been in a boat before?

boater · 03-16-2001, 08:55 PM

ya, this morning

Salmonator · 03-16-2001, 09:07 PM

Please elaborate on the fuel-distrubuting weight compensation system that you have developed for your boat. I'm sure there's a few manufacturers that would pay a pretty penny for this. Mine seems to run a little different with 80 gallons of fuel in the belly and i'm ******.

boater · 03-16-2001, 09:17 PM

you realy have no clue, do you ? ,

Torchman · 03-17-2001, 07:37 AM

Here is an example of extreme porpoising!!!

http://home.pacifier.com/~torchman/qriver.htm

[This message has been edited by Torchman (edited 03-17-2001).]

Salmonator · 03-17-2001, 08:24 AM

Holy cow what a ride! The Coast Guard should shop around a little more next time. That lifeboat is way out of trim...

RJ · 03-17-2001, 09:13 AM

one thing I haven't heard anyone talk about is what type of floatation is under your floorboards.just an example here but a few years back my brother who at the time owned a 19ft willy was really upset with the way the boat was performing he spent a day pulling his floorboards out and removing some 30 trashbags worth of waterlogged floatation,he estimated each bag weighed any where from 20lb to 30lbs each, after the math was done he came up with an honest 600lbs of extra weight taken off his boat,now dont get me wrong I'm not saying everyone run out and pull the floatation out of your boat but it sure does'nt hurt to see what shape its in.RJ

------------------
http://www.fishhawk1.homestead.com

HOGTIDE · 03-17-2001, 01:46 PM

Nice job WILLIE! Bags of flotation that absorb water??? You may have just accidently hit on a drug stash. So thats how they move all that 'bud' from southern Oregon to the Portland Metro area.

Kinda like when John Delorean was hiding 'coke' in the fenders of those stainless steel cars...well, almost the correct story.

boater · 03-17-2001, 03:38 PM

ok, here goes, porposing is caused by putting fish in the cooler on the swim step on your thunderjet.

Joe Schwab · 03-17-2001, 07:38 PM

OK, I'm going to put in my .02 worth and hope I dont get trashed. I had the dreaded porpoise problem with my new 24 Duckworth, 150 HP Outboard. Two things were wrong. From the setup. #1. 14X21 Prop. Way too much pitch! Went like hell but would not stay on plane at cruise and porpoised like crazy. Went to 18 pitch prop. Solved the cruise problem and most of the porpoising.
#2. At the advice of dealer, bent the hull extension very slighly on both sides. Voila!
Boat runs flat with any kind of load and fuel distribution. Remember, aluminum hulls flex and bend and sometimes dont bend back to original shape. Fiberglas normally returns to its original shape. It worked for me.

boater · 03-17-2001, 09:05 PM

salmonator ? other than sitting a bit lower in the water at the dock and taking alittle more power to get on step, what does 80 gallons of fuel do to your boat ? just curious.

[This message has been edited by boater (edited 03-17-2001).]

03-18-2001, 08:48 PM

Now come on everyone let's play nice. Hey boater I really don't think anyone is interested in what happens on your boat when you and your girlfriend sleep on it.
Be Cool!
Stew

03-19-2001, 09:14 AM

Is there anyone else out there who has experienced a change in attitude due to varying weight distribution within their boat?
Is there anyone else out there who has used trim tabs to help alleviate porpoising in their boat? Inboard or outboard?
I have to tell you , Boater, that your comments reflect a very narrow view of the boating industry. Please take some time to put a little thought into your comments before trying to burn others.
I personally have had conversations with dozens (or more) of boat owners with boats of all types who have experienced porpoising problems due to uneven weight distribution within their vessels.
This is a real problem which is easily cured.
Whether you have a TJet or a NRiver the bottom plate extension can be moved up or down manually. I'm not familiar with the Wooldridge solution. Maybe scuttle the boat and use the insurance money for a nice big pickle.

Finn-icky · 03-19-2001, 10:39 AM

Hey Jetstud. Would kindly elaborate some on the best way to adjust the bottom extention. I may need to do this to my boat, but wish to hear from some who knows something about the subject. Thanks for any help on the subject.

jet · 03-19-2001, 12:15 PM

Ok all

lets get this straight to help porposing problems bend the bottoms extensions up? or down? Just a little right? how much of the extension do you bend all of it?

Jet~~~

boater · 03-19-2001, 01:32 PM

refer all boating questions to jetstud, thanks.

[This message has been edited by boater (edited 03-19-2001).]

Salmonator · 03-19-2001, 01:46 PM

So far we have porpoising North Rivers, Thunderjets, Duckworths, Weldcrafts and Jetcrafts, and a Bayliner that needs to be trimmed according to load. Boater, you are claiming all these companies are putting out poorly designed hulls and that sportjets are crap. Did YOU read Capt's post? He distinctly stated that he is running a prop yet you say we are talking jet boats here, not boats with props. Either take your own advice and stop posting or listen to Jetstud and think just a little before you type. I'm sure i've posted some off the wall stuff, but quit claiming to know more than the manufacturers. Yea, you'd think that with the cost of aluminum sleds these days that something like that shouldn't happen. But after reading about all the boats from different manufacturers that do this, don't you think it would be safe to assume that porpoising is inherent to boats in general? Just so you know, my 22 footer with 100lbs of bottomfish in a cooler on the swimstep does not porpoise... Joe

[This message has been edited by Salmonator (edited 03-19-2001).]

boater · 03-19-2001, 03:14 PM

ya i screwed up, sorry for posting here in the first place. just trying to give my opinion, but weight placement is not the only cause of porposing, have a nice day.

WaterDog · 03-19-2001, 07:32 PM

I would have to agree with boater on this

to a point. When I was looking for my new boat, one manufacturer told me that it is very difficult to make every hull exactly the same. Much like car's, each one is just a little different. However, a good and reputable manufacturer will take the boat out on the water and test and trim it before it ever goes on the lot or is delivered to a buyer. It's nice to see zero hours on the meter but I'd rather see half an hour or an hour on it and know everything works.

Salmonator · 03-19-2001, 07:57 PM

I wonder how practical that would be for manufacturers that are several miles from a river or lake to test each boat. What about things like road chips, bumping a rock in the water and scratches while putting her back on the trailer. I wouldn't want to pick up a 40K boat with a dent in it. I know people are freaking out about bending the bottom extension but we're only talking .125 of an inch. Probably couldn't look at it and tell it was bent. I wonder what manufacturers are water testing their boats and what percentage of them are out of trim?

Thumper · 03-19-2001, 08:09 PM

It used to be said that the mark of a truly quality jet boat was whether or not it came with Bennett electrical trim tabs as standard equipment. Only one did, to my knowledge. The JetPace. The Rolls-Royce of jet boats. Gone now because it was just too danged good to compete pricewise. No jet boat is in trim under all conditions. So just opt for some adjustable trim tabs and live happily ever after.

backlash · 03-19-2001, 09:14 PM

I have to say that I would be outraged if my boat was not completely tested before it got to me. As stated above, there are way to many variables as these boats are all built by hand, we all know about human error. If a manufacturer can feel good about charging these inflated prices, he damn well better make sure it runs as advertised. Also just a guess here but these guys probably are'nt going to scratch or dent up the boat on a 30 minute test run. I am happy to report Alumawelds boats all hit the river before being shipped to the dealer.

Salmonator · 03-19-2001, 09:57 PM

T-Jet did take us out for a cruise before we left Lewiston, as I would imagine they do for all new boats but the initial run is with the buyer. I was thinking of it as more of a basic "how to" run, but now that I think about it, it would have served as a trouble shooting run just as well. Had the boat porpoised , i'm sure they could have re-trimmed it back at the shop but it wasn't needed.

HOGTIDE · 03-19-2001, 09:57 PM

On Porpoise...to On Purpose.

So I buy a brand spanky Alumaweld SuperVee Pro. Love the boat. But at full throttle, with me at the tiller, my merc, my lil merc and 45 gallons of fuel in the floor tank, all hangin' near the transom, my new boat porpoises quite a bit on flat water.

I decide to brave the wilds of the upper Clack, of course always going about a quarter mile further than I should at low water. Well On the way downhill (all you true sledders already know the 'downhill' story) I smack a mid-stream boulder about the size of a 1959 Chrysler. 'Bout throws my partner out the bow...like we are airborne. Plane that puppy out and head for the barn.

The don't-wanna-look inspection finds that I have left a 2' long dent in the hull near the rear. Planning to fix it soon. However, I notice the next couple trips that my boat actually runs flatter, no porpoising at all, no matter what the load setup.

I decide to leave this CAD (Collision And Disaster) designed boo-boo in the hull, on purpose. I deemed it my Turbo-Dent. It improved my boat's performance. True Story!

I wonder if Alumaweld is looking for 'Field Adjustment Specialists' to test their new boats? Crashing is kinda fun... after you find out that you lived.

[This message has been edited by HOGTIDE (edited 03-19-2001).]

new boat · 03-19-2001, 11:04 PM

No, don't want to buy a bridge!! Don't need to put the cooler on the back, have room inside!! Yes, I did bend the bottom extension on my boat. Down by approximately 1/8th inch, three inches each side of the keel. Spoke with Thunderjet before it did the job. After reading all the bad things about TJ's, was afraid I might break my boat. TJ assured me I would break the metal before I broke the welds. Used two large crescent wrenches next to each other to do the bending. Did try having my buddies move to the front of the boat before I did the bending. Made the boat rider better, but my buddies thought it was king of cold riding in front of the windshield. Boat rides great now. Maybe the original problem was catching too many fish. The fish box is towards the rear and the fish are heavy!!!

TH · 03-19-2001, 11:51 PM

Spray in foam from Willies.... I have heard too many complaints frm guides/sporties a like thathave been very disappointed with the foam. Most have ripped it out after a year or so

As I heard from Mike at Willies, it is not recommened from boats over 18ft.

I stayed away from it in my 22ft predator.

TH

www.thcustomrods.com

Killertraylor · 03-20-2001, 07:25 AM

Speaking of test driving boats - that invites another question - how many of you follow the recommended break in instructions in your manual? Both boats I've bought, one from Weldcraft and one from North River had big Yamaha outboards on them. A 200hp on the 20' Weldcraft and a 250hp on the 23' NR. When both were delivered to me, the dealer says with a proud smile - boat runs awesome! Top speed of 54 mph! I'm sitting there thinking "what the hell are you doing?" The manual says not to run the motor at full throttle until you have at least 4 hours on the motor, and then, only do it for about 1 minute at a time until you have 10 hours on it, and then you can run it as you please. On the other hand, I know a lot of guys who swear by running a motor full throttle as much as you possibly can during the first 10 hours as it breaks the motor in better. I lean towards following the manual myself.

boater · 03-24-2001, 05:51 PM

[img]images/icons/smile.gif[/img]

[ 03-24-2001: Message edited by: boater ]

RJ · 03-24-2001, 06:10 PM

Hogtide I'm curious where is that dent located (specifically)RJ

HOGTIDE · 03-25-2001, 07:14 AM

RJ,

It is located at the rear of the boat, about the last 2' of the hull, just right of center. Probably only 1.5 inches deep, but long. Doesn't cause cavitiation or anything..just flattens the boat out when she runs.

Hey ...gotta a new sled. Lets run the Deschutes!!! We'll just keep running RattleSnake til I get 'er tuned perfectly!

RJ · 03-25-2001, 09:26 AM

Thanks for the reply HOGtide I have seen this same thing happen before on some other boats so I think it may be more than coincidece sounds like you stumbled upon the ultimate Trim tab (no tools required) [img]images/icons/grin.gif[/img]

RJ · 03-25-2001, 10:36 AM

This is called the tiller handle Boogie

[ 03-25-2001: Message edited by: RJ ]

HOGTIDE · 03-25-2001, 04:14 PM

That's cool!!! How do you guys do that stuff?

boater · 03-28-2001, 06:29 PM

what is porposing ? dont ask me, i`m stupid.