30hp vs 40hp speed

If a 40hp weighs 40 lbs more than a 30 hp, will the extra 10hp push a boat any faster ? This is on a tin 16 ft v hull rated for 40hp, dry weight 250 lbs, loaded maybe 1000 lbs total. Pondering the expense vs the gain.

Came across a calculator and punched in different numbers and got no more than 3 to 5 mph difference. You'd think it would be much more than that.

https://www.hhscott.com/evinrude/docs/bslac.htm

...which motor or motors?..

These are mid '80s Mariner tillers.

Had the same debate myself not long ago on my 16' Naden big fisherman. Naden on Wikipedia says 45 hp (who ever made one of those) I went with a 35 hp Johnson which I'd think is closer to 30 hp now that is measured at the prop. For me the weight (less than 120 for my pull start) vs what a 40 weighs. Tohatsu had a really light one but the newer ones are all heavy as heck. That old Johnson will push the 290lb boat with 3 guys all over 225 plus trolling motor, battery and my obsessive fishing buddy's oversized tackle box.... you get the picture. Jumps up on plane with no plowing and pushes it as fast as I need it to go. And I can hang the motor myself. With just two of us it flies! No gps speeds but I've owned enough boats to know and I won't be searching for that extra 2 mph because it doesn't need it. Hope this helps.


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Crestliner c1652v (tunnel).1994? DT Suzuki 40hp 31mph -1986 30hp Mariner (yamaha made) 27 mph...current motor 30hp...the prop is pretty dinged thinking it's a close to a 12 pitch. When I carry a heavier load(camping gear acouple more people)with the 30 I switch to a 10 (93/4) pitch...it will plane with the 12 but slow...jumps right up with the 10 and only looses a couple mph. I could notice the power difference between the 2 but the lakes up here are small and in less I do more salt water fishing the 30hp is fine.

I was looking for an '83 35 hp OMC but the 30 Mariner turned up first and my mechanic said those Yamaha Mariners were well made. NADA says it weighs 112 lbs and a 40 hp weighs 143 lbs so the difference is only 31 lbs but still gives only 3-5 mph more.

83 Johnson is what I have. The big difference would be grunt. How much you could load your boat and still plane easily and attain top speed. I had a 20 that pushed my boat perfectly with me and my daughter. When I added a third, it slowed considerably. The 35 works wonderfully on it. 10x13 prop. Depends on how you load the boat.


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143 sounds awfully light for a 40. Most older 40's were around 175 or better. 4 stroke over 200.


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Extra torque is always good. I thought about a 40 OMC but they're much heavier. I've heard you may not have to change out the steering bracket on those older Mariners to convert one to tiller.

What 40hp motor did nada say was 143 lbs?Yamaha did make a 40hp 2 cylinder sold as Mariner or Yamaha enduro but it weighed 160 lbs.I think a 3 cylinder Yamaha 2-stroke(135 lbs) would be a good match for your hull not sure how much faster it would be but will push a load much better than your current motor.

3 cyl 40hp motor would weigh more than that. As far as I know, the tohatsu/nissan m40c was the lightest 40 hp ever. If I ever come across a short shaft tiller model, I'm gonna buy it.


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I get motor weights from the NADA site:

https://www.nadaguides.com/Boats/1985/Mariner/Outboard-Motors

Took the boat out for the first time today with only me and the motor and the 25 Evinrude on it now is really all it needs (except it's rope start) so the 30 will be that much more fun when the mechanic is done with it. A tiller handle is on the way for a 40 but I may hold off on buying a 40.

I was refering to the 30hp yamaha 3cyl.

Last week I came across a 1984 Evinrude 35 hp two hours away after eyeballing a '96 40hp 2 cyl Tohatsu four hours away. It gives up 5 hp but weighs 30 lbs less which makes a lot of difference when you move them around by yourself.

Make sure your OMC doesn't have clutch dog issues.

I'll find out this summer. It looks like it's been used a lot but it cranked right up and has a new prop and coil packs.

Yep pretty much 3-5 MPH depending on brand of engine, the higher and bigger boat you go you will only get 1-2 MPH for every 10 HP.

Sometimes you'll get better MPG/GPH with the larger engine being you can cruise at lower RPM's but it won't be a great gain.

I'll check around if I have some time and see if I can bring up 2 same boats with various engines on them so you can compare apples to apples.

OK so here are a few links to look at:


40 vs 50 3 MPH upswing but less MPG

https://yamahaoutboards.com/sites/default/files/bulletins/bulletin_4stroke_midthrustjetport_al_sa6ac7.tmp.pdf

https://yamahaoutboards.com/sites/default/files/bulletins/bulletin_4stroke_midthrustjetport_al_alm_classic165cs_f50tlr_2011-05-26_alm.pdf

30 vs 40, 7 MPH upswing (amazing amount IMO) and 2 MPG improvement with the 40. Only other change is the 40 is slightly lighter when tested and is a SC not a tiller.


https://yamahaoutboards.com/sites/default/files/bulletins/ALM_Escape145Tiller_F30LA_2013-09-10_ALM.pdf

https://yamahaoutboards.com/sites/default/files/bulletins/ALM_Escape145CS_F40LA_2016-06-01_ALM.pdf

In 1985 the industry hp ratings went from crank hp to prop shaft hp and the 35 became the 30 or so I am told. The later tohatsu 40 will be a true 40. The difference would be significant I would think. I have an 83 Johnson 35 and love it on my 16' boat. Good dependable motor with parts being readily available.


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Interesting. Guess I'll be comparing speeds if I can find an app that will work more than once.