Re-power advice...

[philmay75]

Hey folks,

I've got a 25'9" Bennington pontoon (no strakes) with a 90hp 4-stroke merc on the back. With the wife and I alone, it will run 21/22, and tends to run close to max rpm. When we put 6 of our friends in it (isnt this what the big toons are for? :joyous: ) we run about 15 mph. Also, when we ski off it, even with 2 adults in, and one adult skier, we see that just a little more power would take the rope slack out of the wide turns. Last, I think the motor may need to be dropped a bit deeper because depending on the chop of the small lake, it cavitates, or maybe ventilates. That's the background, heres the question...

I found a guy that has a long 25" shaft 125hp similar year 2-stroke that wants to trade for my 20" 90hp 4-stroke, because 25" is too long for his 18' ski boat. I'm fairly new to boats, and am wondering if I might hate this decision later.

Will the 5" longer shaft matter? My 20 inch is mounted 1 hole from as deep as it will go. So I assume I can just mount it on a higher hole.

Will I notice a difference in performance since the 2-stroke is about half the weight of the 400# 90hp 4 stroke.

Will a 2-stroke on a pontoon perform better or worse than a 4-stroke from a torque or top-end power perspective?

You think the noise difference would be unbearable?

I'd have to make a significant drive to make this even swap power-up trade, so I am trying to research a little before I commit. I'm grateful for any comments and personal experience shared.

 

[Dr. Evil]

Re: Re-power advice...

I couldn't imagine even entertaining the idea of trading from a 4s to a 2s. I assume yours is EFI.
I'd look to make sure you have your boat properly sorted before I'd start swapping engines. How clean are your tubes? How about underskinning? Its not like the underskinning wont help later if you do decide to swap motors.
My last boat had a Force engine on it. My current has a 4s Yamaha. I cant begin to describe how much happier I am with the new one.
FWIW, my 20' does 16mph (GPS) with 4 adults, 4 children, top up, 2 coolers and all gear. My Yamaha is a T50 with a 13 5/8 x 13 prop.

 

[philmay75]

Re: Re-power advice...

Dr. Evil,
Thanks for your reply. My 2000 90 is not EFI, actually. Its a 4-carb system. Was told by a marine mech that it is one of the motors that yamaha made for merc before they had a falling out, and that's why the price of a single carb rebuild kit is $150. :blue: All the parts for my particular motor are crazy high. I had a johnson that I replaced both entire carbs on for less than a single rebuild kit on this one.

Honestly, its more about the opportunity to make an even-trade power up, than a desire to move from 4 to 2-stroke. from what I've seen, powering up to a 2-year newer 40% more hp motor isnt usually a low-cost endeavor. I think a 26' benny is just too big a boat to actually plane up on a 90hp, especially its current setup.

I've considered underskinning, just havent priced it out. Im sure that would help, as we do feel the grab of the water on the crossbeams.

Also considered strakes or a 3rd toon, (in which case, that 25" shaft or more hp might be of benefit). I asked a couple of bennington dealers in my area for prices, but no one wants to bother pricing out a 3rd toon or strakes for me. They all want me to trade it in for a new one. haha

 

[The Rooster]

Re: Re-power advice...

Phil, you're probably looking at approx. 3-4 mph increase. You'll burn more fuel, but nothing drastic. You can work w/ the 25" height even if you require a manual jackplate. May hurt future resale value. If you're not going to keep the barge for a while, I wouldn't waste the time & effort, but may be the cheapest option for now. Not sure if your current throttle cable & electronics will marry right up to the 125. Generally speaking the 2-stroke will out perform the 4-stroke from idle to top end. Good luck !!!

 

[lakegeorge]

Re: Re-power advice...

I believe that you will get a lot more mph than 3 or 4 that being said, there's nothing wrong with a 2 stroke engine. I also think it will help future re-sale as 90hp is low for that size boat.
If the cables & everything fits I would do it. You obviously aren't to happy with your set-up so why not do it.
It probably wouldn't hurt to talk to the local dealer and see what they think about the retro fit.

 

[crb478]

Re: Re-power advice...

The 25 inch shaft is too long for your boat. You would have to use a jack plate which will add to the cost. Also dropping your current motor one hole can make a tremendous difference in handling or cavitation. I would look for a bigger motor with a 20 inch shaft as the 90 is probably a little small for you boat. I also agree that underskinning would be a wise investment before you start changing things up. Since you know that your motor is kind on a rare unit try to sell it to someone and then pick up the best motor you can find with a 20 inch shaft.

 

[MaPaHa]

Re: Re-power advice...

I just converted my 150 hp Johnson to an X-long shaft (25?) from the standard long shaft (20?) using a Bay Kit extension. It was a good move no doubt. I did install a manual jack plate from CMC which gave me the wiggle room to get it set right. My problem was the 20 inch motor was set all the way down and would ventilate way before it was trimmed out and would loose grip in the turns. It would not trim enough to keep the bow up. I?ve got to a workable setting where the cavitation plate is just below the water line which performs well. Also, the 5 ?? set back gets it in cleaner water.

I?ve never heard anyone say they have too much HP on a pontoon, but many comments the other way. It is hard to estimate how much gain you will get with the change and as mentioned there are some other things you can do to help. I?ll start from the low end and work up because I don?t have any idea how much you are willing to spend to get to the point where you can ski well.

I?m a firm believer in the under skinning. It helps in light loads on smooth water and it helps in heavy loads in rough water. There?s not a condition it doesn?t help.

Getting the max RPM?s right with a prop is important but? there?s more that can be gained by choosing the right prop than just the hitting the RPM?s. I would suggest looking at a premium 4-blade prop that?s made for pontoons. I talked to the folks at Power Tech and they helped select a ?big ear? prop that?s just right. It was one of their Off Shore series. There are a lot of opinions on 3 vs 4 blade props but it seems that 4-blade props are known for stern lift vs 3-blade do better at bow lift. You might lose a mph with a 4-blade but you will gain mid range performance and throttle response such as tubing speed and cruising speed. Get ready to spend $350 ? 500 bucks.

If you still aren?t satisfied then I would look at adding a Pontoon Water Glide which will do everything they claim. Been there and done that. Unbelievable difference in speed and turning but you?ll spend some money.

Adding strakes will also help a great deal but before you do, send me a PM and I?ll tell you about ?adding lifting strakes gone wrong?. Just get a pontoon welder that?s done it. The lifting strakes will be cheaper than the pontoon glide, but more risky.

My current configuration is: 23 ? feet tubes, Tri-toon, lifting strakes on all three tubes, 150 HP Johnson, X-long 25? shaft, jack plate, under skinning and a 4-blade off shore prop. I can almost hit 40 MPH GPS with the bow up and water spray about half way back. The boat turns well for tubing and no problem with skiing speed. It has a hole shot like crazy to the point where I?ve been asked to back off the throttle a bit getting an adult skier out of the water.

We went out on the river here in Little Rock on the 4th to watch the fire works and the boat was loaded heavy in the front and it still picked up the bow without blowing out. Love the 25? X-long shaft. Just get a jack plate so you can get it set right.

Well thats 5 years of experimenting in one page. Hope some of it helps.

 

[The Rooster]

Re: Re-power advice...

+1 ^^^

 

[philmay75]

Re: Re-power advice...

Thanks, everyone for the great comments. Regardless of what else, I am going to underskin it. Started looking yesterday at the cost......I did not know that aluminum is a precious metal. :laugh:

As to the motor, the guy has a jack plate he would throw in. Would just need to decide if I want to make the 25-hour round trip drive to get it.

Another wrinkle is I took a look at the coast guard plate today, thought it was 125 but...max is 120hp. New motor is a 125. That sux because while I am not aware of any law against overpowering in TX (and 5hp is not much of an overpower), I am not sure if I could insure it. :facepalm:

I may see where strakes and the underskinning get me.

Thanks again for the input.

 

[lakegeorge]

Re: Re-power advice...

Thanks, everyone for the great comments. Regardless of what else, I am going to underskin it. Started looking yesterday at the cost......I did not know that aluminum is a precious metal. :laugh:

As to the motor, the guy has a jack plate he would throw in. Would just need to decide if I want to make the 25-hour round trip drive to get it.

Another wrinkle is I took a look at the coast guard plate today, thought it was 125 but...max is 120hp. New motor is a 125. That sux because while I am not aware of any law against overpowering in TX (and 5hp is not much of an overpower), I am not sure if I could insure it. :facepalm:

I may see where strakes and the underskinning get me.

Thanks again for the input.

I honestly don't think that you have enough hp for strakes. The underskinning will help with the thumping that the waves cause.

 

[Bamaman1]

Re: Re-power advice...

You've received some very solid advice here--right on the money.

And I agree that the big Bennington does need strakes, but you'd be wasting your money without putting 150 hp on such a heavy hull. The factory can provide your dealer with a set of strakes, but it takes a very good welder to install them (and keep from burning thru the hull.) Most dealers are in business to sell new boats, not adding strakes. And there's no boat dealer that has a welder good enough to do TIG welding.

You didn't say what year and model your boat is. If it's a high line Bennington, have you considered a complete repowering with proper horsepower? I always say put the maximum horsepower that the plate allows. You can get a new Mercury 125 hp Optimax for $8K. A 115 hp Merc. 4 stroke is about $8K and a 150 hp FourStroke for about $10K--not including installation or controls. A Yamaha F150 is more like $13k online.

You do have some options. The bigger Benningtons are somewhat rare boats, since most sold are 22-24' boats. But I can tell you that 90 hp on any pontoon is very marginal if you're into tubing or water sports--much less the big hull.

 

[MaPaHa]

Re: Re-power advice...

I have to agree with Bamaman1 that the strakes and larger motor should be looked at as a combination. The strakes will add lift but they will also add drag and without the horsepower they will not be as much benefit. They might help some with you're existing motor but not near as much as with the larger motor.

In an extreme example consider that you could put 747 wings on a small twin engine airplane and although the wings have the capability of much more lift, the plane does not have the horsepower to utilize the additional wing surface. I know that's extreme but the concept I think still applies. The amount of added lift needs to be in relation to the added HP.

On the other hand, most of my projects are a work of art over time. I’ve been known to do something like adding strakes now and getting what I can and then I’m set for when I have the opportunity to make the motor change. I never have a problem spending money on a better foundation even if I don’t build to the max now. I believe you will not be hurt by the strakes with you’re existing motor and you should get some improvement, just not as much as with the larger motor.

When I had mine added the welder burned holes in the pontoon behind the strakes where you can't get to them to fix. The young welder that did the work is no longer with the welding shop and the owner is working with me to make it right. We are going to wait till boating season is over so he can work with it.