Speed/HP boost for towing kiddos

[tmcelveen]

Current setup is a 2012 Bennington 20', 2 toon with a Yamaha F50 4 stroke, AL prop (not sure pitch). Everything pretty stock.

Our main use is tooling around the lake and towing the kids on inflatables but we're just a tad underpowered for being able to get some good bounces and a little air under the inflatables (they're 9 and 6 have no trouble holding on no matter what I try ), so we're hoping to be able to eek out a bit more.

I've done a lot of reading but don't have enough practical experience to translate the options into real world results for what we're looking for. Here are the options I've found so far and please feel free to educate me on any I've overlooked:

1. Underskinning
2. Poly3rdTube
3. Water Glide
4. Upgrade motor to max plate spec (70HP) - the 70 only weighs 2kg more than the 50 so I'm assuming I could get decent improvement since I'm adding HP and not much weight
5. Upgrade motor disregarding max plate spec (90-115HP) - decent weight increases over the 50HP, so I'm not sure how much actual gains I'd see
6. Poly3rdTube with upgraded transom and upgraded motor (90-115)
7. New prop (not sure of existing pitch, but I know it's AL)

Thoughts on any of these or combination? Any ideas I missed?

Thanks in advance!

 

[racerone]

Bigger motor.

 

[jbcurt00]

Bigger motor.

Agreed, but w in limits of max rated hp.

And need to know max WOT RPMs w what pitch/diameter prop

 

[tmcelveen]

Agreed, but w in limits of max rated hp.

And need to know max WOT RPMs w what pitch/diameter prop

Right, in doing the research I realized I need to measure the WOT RPMs, especially if I want any sort of quantifiable measure of improvement.

So, is the 50 to 70HP a noticeable improvement? On paper it seems to be, 40% HP increase with negligible weight cost, but I don't know how that translates when you add in the hydrodynamics of pontoons.

 

[HotTommy]

In theory a 40% increase in applied power will yield an 18% increase in top speed. That is likely 2-3 MPH in your case. ... The most practical things you can do to increase speed are to decrease weight and aerodynamic drag. For example, leave excess adult passengers on shore and take down the bimini top while tubing.

 

[tmcelveen]

In theory a 40% increase in applied power will yield an 18% increase in top speed. That is likely 2-3 MPH in your case. ... The most practical things you can do to increase speed are to decrease weight and aerodynamic drag. For example, leave excess adult passengers on shore and take down the bimini top while tubing.

That's super helpful! Dumb question, but is 2-3 mph a noticeable difference? I've never measured our actual speed before...but I guess on paper that's ~10% increase in top speed? I know it's all fairly subjective.

We got the boat so relatively cheaply that trading in for a bigger boat (larger max HP) doesn't really make good financial sense.

 

[HotTommy]

I believe 2-3 MPH would be noticeable, but it won't be enough for the teens you'll have in a few years. ... I love having a family activity that all the kids enjoy doing. I think you'll want to upgrade to a bigger/faster boat in a few years. Prices are really high right now, so I suggest you set your sights on something affordable in a couple of years. In the meantime I wouldn't spend a lot on an engine upgrade for the current boat if it were mine.

 

[tmcelveen]

I believe 2-3 MPH would be noticeable, but it won't be enough for the teens you'll have in a few years. ... I love having a family activity that all the kids enjoy doing. I think you'll want to upgrade to a bigger/faster boat in a few years. Prices are really high right now, so I suggest you set your sights on something affordable in a couple of years. In the meantime I wouldn't spend a lot on an engine upgrade for the current boat if it were mine.

I definitely appreciate the honest input. It's a tough decision for sure.

 

[Rabbit929]

Ive found that 40hp is minimum for a pontoon, and 50hp is just a small step upward of the bare minimum. If your max motor capacity on the pate is 70 hp, that toon is built for putt putting around and not much else.

I will say my new 2021 21ft sylvan, with the 25 inch diam-tubes, and a 90hp yamaha, loaded down with 7 adults, 8 kids, and 3 people on a 3 person tube, will pull 16-18mph. just enough that in the right wake i can dump em! (i was super happy about this.)
The larger diam tubes they are putting on these newer pontoons make a world of difference. Mine is rated for a max of 115, and i REALLY wish i just bit the bullet and spent the extra couple bucks for the max hp motor.

In your case, i would be looking for anything 90hp and up. it seems 90hp is about the best "minimum" size setup for tubing, and if it were a 150hp would do everything you want it to and more, the thing i liked about the 90hp yammy though was its the lightest and strongest motor with the biggest alternator in its weight class. Even so, I still wish i went with the 115hp so i could stop thinking "what if..?" lol

But to make due with your 50 hp your best bet would be to strip off as much weight as possible, and get an appropriete prop fitted for towing.

 

[ahicks]

I think this call may be about your tube size. If they are big enough to hold a heavier 90-115 (25"+) then that's likely a good plan. A motor like that should give you enough authority to entertain the kids.

OR

Maybe consider a deck boat in your future. One with a 4 stroke outboard. They'll cruise nice and slow while being dead quiet, but when it comes time to entertain on the end of a rope, they're PLENTY capable even when the kids grow into their teens. Great dual purpose boats that work for about anything - until the water gets rough. That big wide hull that does so well skiing can be a pretty rough ride when it gets choppy. You'll need to slow way down.

 

[tmcelveen]

Appreciate all the great advice, guys!