115 4-stroke adequate for a 21' hull?

[1pump]

I'm in the middle of spec'ing a new 21' center console aluminum boat. I don't want to go into detail 'cuz I'm sure the dealer will see this post.
Anyway, I want a 150 (at least) but Merc doesn't make a 4-stroke in that range. They jump from 115 to the 200 Verado, and that's a $6K jump. The hull is rated for a 200, has a 6' bottom, 10 degree deadrise, and with a 115 it will weigh in around 2200-2300 lbs (and it's a prop, BTW). The sales guy insists that a 115 will be more than adequate, but I'm skeptical. It's a work boat, so speed really isn't an issue, but it needs to have good towing power. It doesn't need much range, so fuel economy is a non-factor. But for many reasons it has to be a 4-stroke.

Anybody here running a similar combination? I'm curious to know what kind of MPH you're getting.

[HOOKUP]

I would expect that rig to run in the high 30's might even get in the low 40's.

[MacEFL]

I have 115 Merc on a 19' Smokercraft Osprey. I don't know what it weighs but with a 9.9 on the back, 40 gals of fuel. Two guys at 225 each, she eeks out 40 GPS.

[TheRogue]

Sounds UNDER powered to me.

Mercury is really missing the boat with no 150!! Look at the popularity of the Suzuki 140. Same with the Honda 130.

I know someone with a Seahawk 20' and a Yami 115....no performance demon, that's for sure.

Get your boat....then go elsewhere for the motor.

TR

[Tacklebuster]

I have a friend with a 21' Boulton with a 115. He 100 percent regrets the choice in power. He too was convinced the 115 would be plenty but didn't get to demo because there were none set up like that. He is in the process now of loosing a wad of cash just to get into something that will push his boat better.

Whatever you do, demo something of the same nature before buying. Have the dealer type a condition in the contract that sale pends on customer satisfaction with demo on boat before delivery.

[5-Cents]

I would say that's under powered and I have never heard anyone ever complain about too much power. If it's rated at 200 you should go for the bigger unit, the extra $6000 will only be a few $$$$ a month if you are financing and you will be much happier.

[1pump]

Thanks for the replies. This is a cash deal, and there's barely enough room in the budget to get the 200 Verado if I get a good deal on it. The good news is that I'm not the one paying for it, but the bad news is that I'm responsible for ordering it. If the boat can't do the job, then I have to stand before The Man and explain why.
The dealer has been good to work with so far, so we'll see how this pans out.
One thing about the Verado- that thing tips the scales at over 650 lbs!! A freakin' inboard doesn't weigh much more than that! I don't mind the extra overall weight of the boat, but that's a lot of strain on the transom.

[corrirod]

115 sounds underpowered to me and if you have the funds you won't be unhappy with the Verado.

[foxer]

Find the motor you really want. Then tell them to get it for you. If not, go hull only. If its who I think it is, the can get you any motor if it's going to be the deal breaker.

[Tacklebuster]

One thing not mentioned here is application. What exactly is the boat going to be used for? You may not require anything with more "go" if it is just being used to get to point A to B. Maybe the 115 would work in your application

[fop]

Well I'll tell ya what. I have a 20 and a half foot Willie Predator 6 foot bottom and 27" sides with a 100 HP Yamaha 4 stroke prop it hauls hiner. Just can't see any reason that it wouldn't work as good with a 21'er unless it's a big heavy hog type boat.

Never have put it on a scale so not sure of it's weight. I'm sure it will go around 40MPH with 3 or 4 of us in it. And, I never open it up and see not a reason why I should have to. Also the 4 stroker is so good over a 2 stroker. Fish all day on 6 to 7 gallons of fuel. But alot of that time is on the 4 stroke kicker.

Mine is a tiller and did I tell ya I love it? Well I do!!

fop

[Draggin' Bait]

The Yamaha website has a LOT of engine/boat combos tested for speed and fuel efficiency. You might try scanning it. You aren't likely to find an exact match, but you will probably find some tests with similar hull/hp combos.

[Fish mojo]

Way underpowered. I test drove an Alumaweld Intruder 20' with the Merc 115 4 stroke. I would have been embarrassed if I was the salesman. If you are looking at a certain brand that is tied to Mercury, try looking at another dealer who rigs his boats with other motors like Honda or Yamaha. The Verado is not an option for this (too heavy and too expensive).
I think there is a dealer in Salem who does Alumaweld with Honda if that is what you are looking at.

[hogliner]

Go with the 200 man

[Salmonator]

It's possible that with the 10 degree deadrise the 115 can plane the boat fast enough to make you happy. I had an 18' alumaweld flatbottom with a 115 jet. It popped out of the water no problem. Like already mentioned you're only going to know for sure if you get a demo. If they're confident in that 115, they'll give you a demo.

[Tinman]

There is a great rule of thumb that says you need one horsepower to push 30 pounds of boat at 30 mph. Here is how it works. First add up the total operating weight of the boat, including hull, motors, fuel, accessories, ice, passengers etc. Include everything. Then divide this weight by 30. The resulting number is the motor horsepower required to push the boat at 30 mph at wide open throttle.

For example, let's say the boat and motor weigh 2300 pounds, and the fuel, accessories, gear and people add another 1000 pounds for a total of 3300 pounds. 3300 divided by 30 is 110 horsepower. So a 110 horsepower motor at full throttle will push the rig at 30 mph.

A flat bottom will be slightly faster, and a deep V slightly slower, but the rule is pretty good.

My source is the excellent Powerboat Handbook, by Jim Martenhoff, circa 1980.

[Big Stick]

I drive a 19' Duckworth Pro Steelheader with 100 horse Yamaha 4-stroke power.

For applications of interest to me(Hunting/Fishing in SE Alaska),I think it is a fair match. The fuel economy is outstanding,the motor trouble free and the performance is OK,as I can cruise 35mph at 4200RPM with a modest load onboard.

Were I contemplating a larger hull,I'd poke more motor on it,just to have the spare ponies in reserve. Extra power is a nice comfort on big water,in changing weather.

IMHO,the 115HP on the 21 footer is bare bones minimum and one wouldn't be on the water long,before he craved more ponies........................

[Critr Gitr]

21' Boulton Sea Skiff w/ 115 Yami 4 stroke 19" pitch
3500 # boat motor/trailer loaded so figure 2800# of just boat + motor
3 guys & gear it pushes 36-40 mph via GPS depending on trim

you are lighter - I think you are fine = with the price of the 115s vs the 150 you can get twins for just a little more

if nothing else you can get a lot of boat jewelry

drive it and sea :smile:

[1pump]

you are lighter - I think you are fine = with the price of the 115s vs the 150 you can get twins for just a little more

Twins? Noooooo......my boss almost bought a 22' Almar with twin 135 Black Max Mercs and I'm relieved we didn't. It was a nice boat, but I would've been responsible for maintenance. I have enough headaches as it is. Twin 4-strokes would be nice, but some of the people I work with can't even drive a single-engine boat, let alone twins. And everybody has to be able to use it.

[Mo Money]

Go big.When theres a will theres a way.Lifes to short to settle for less!

[Kalamajack]

I'm running a 115 Yamaha 4-Stroke on my 20' sled and it tops out at 38 MPH (limited by drag). With just me in the boat, 38mph... With 4 fat beer drinking machines onboard, 38 mph.

Are you sure you want a Mercury? Go with Honda or Yamaha...My Yamaha is Fuel Injected and if I run 30 mph, I can go 350 SM on a single 38 gal. tank.

[biederboat]

My "open" (consoles, no winshield) 21' Starcraft had a 115 2-stroke and would top out at about 35, pretty good power. My boat is a bit lighter than yours but more deadrise and has rivet heads on the hull so maybe that's equal. A 4-stroke motor is a bit heavier. I don't think you'll be disappointed but, if you were considering a Suzuki, I'd say spend the extra and get the 140. Mine has a 140 2-stroke on it now that, so far, I'm very pleased with but the 115 was definitely adequate.

Biederboat

[Plumber John]

I bought a Thunder jet 20ft with a 140 suzuki. the dealer also said a 115 would do, I insisted on the 140 and got it. I ran into a fellow with a boat like mine except he had the 115 he said he wished he had gotten the 140. Im glad I did.