Boat Length effect on performance question.

[ressless1]

I am considering a longer boat, and see 90 hp motors on several different length boats.

I know that I can paddle a long, 16 foot, kayak faster than a short, 10 foot, kayak, and the longer kayak will glide faster and farther than the short one, even though it weighs more. But, the short one can be turned quicker.

Speed wise, will a 90 Hp motor have similiar performance on a 20 pontoon, or a 22 footer, or a 24 footer?
Or, with the same 2-4 person load, how is pontoon boat performance affected by length?

 

[lakegeorge]

Re: Boat Length effect on performance question.

The simple answer is that the longer pontoon will run slower with the same size motor.

 

[EGlideRider]

Re: Boat Length effect on performance question.

+1^

 

[The Rooster]

Re: Boat Length effect on performance question.

+1^

Agree with the others !!!

 

[steelespike]

Re: Boat Length effect on performance question.

The kayak moves at displacement speeds the beam to length ratio works at those speeds.
I believe the relative increase in weight is heavier in the pontoon.
There is a lot of disruptive components on a pontoon to disturb the flow around the boat
And the longer the boat the more disruption.
Generally a pontoon will be more economical around displacement speeds than a planing hull.

 

[5150abf]

Re: Boat Length effect on performance question.

More length also means more furniture, deck, crossmembers, ect which all equal more weight which kills speed so if you got a bigger boat and removed alot of the furniture it would be about the same speed but that is silly.

Agree with Steelspike, your comparison is apple and oranges as the 2 boats are completely different, i don't know that the speed difference is enough to offset having a larger boat though, for me having the extra couple feet of boat would be worth a few mph.

 

[Blank-N-Ship]

Re: Boat Length effect on performance question.

I am considering a longer boat, and see 90 hp motors on several different length boats.

I know that I can paddle a long, 16 foot, kayak faster than a short, 10 foot, kayak, and the longer kayak will glide faster and farther than the short one, even though it weighs more. But, the short one can be turned quicker.

Speed wise, will a 90 Hp motor have similiar performance on a 20 pontoon, or a 22 footer, or a 24 footer?
Or, with the same 2-4 person load, how is pontoon boat performance affected by length?

If you took the figures into a propeller selector (online calculator), entering in the weight of each pontoon length for a Leisure Kraft Pontunes boat, say, in the range of 18-26 feet then here are the calculated speeds for a Suzuki DF90 engine:

Figures Calculated from Mercury Prop Selector Page:
18' -> 23.5MPH (15.0-pitch)
20' -> 22.5MPH (14.8-pitch)
22' -> 22.5MPH (14.8-pitch)
24' -> 21.7MPH (14.3-pitch)
26' -> 20.9MPH (13.8-pitch)

As was mentioned before, the furniture arrangement and other options will affect the overall weight but when it comes down to it--on paper anyway--it looks like the additional weight doesn't equate to a huge difference in top speed for the same engine at the 90HP mark. In fact, a longer pontoon length means that the same weight load would be distributed across a longer log; each pontoon could be out of the water slightly higher than a similarly-loaded shorter boat. The real-world figures for top-end speed will be more or less than theoretical... in fact, all these numbers look low for what I know to be reality. If your pontoon boat manufacturer's furniture is overly-heavy then yes, an additional two feet of furniture might be a big trade-off in speed from the same engine.

So I would weigh in by agreeing with your original idea/experience with kayaking (or my own experience with downhill snow skiing) with a bigger kayak/ski. There are some advantages in spreading things out over a longer base.

 

[ressless1]

Re: Boat Length effect on performance question.

So, if I stick with a 90 HP, a 2-3 drop in top speed if I move to a 24 footer from my 20 footer, could be expected. I could live with that.

I realized this past summer that the pontoon is a social boat rather than a performance boat.

Its best function has been bring family and friends together to create lasting memories. And that is my main reason for thinking of a little longer boat, with a little more comfort and convience. Mainly, rear entry, a changing room for the ladies, a pylon to keep the tube rope out of the water, and a 4 stroke, or at least a newer design 2 stroke.

Pulling the kids on a tube was great, but so was the wine, cheese and a sunset.

 

[steelespike]

Re: Boat Length effect on performance question.

If your getting a new motor check out the Evinrude Etec.

 

[Blank-N-Ship]

Re: Boat Length effect on performance question.

So, if I stick with a 90 HP, a 2-3 drop in top speed if I move to a 24 footer from my 20 footer, could be expected. I could live with that.

I realized this past summer that the pontoon is a social boat rather than a performance boat.

Its best function has been bring family and friends together to create lasting memories. And that is my main reason for thinking of a little longer boat, with a little more comfort and convience. Mainly, rear entry, a changing room for the ladies, a pylon to keep the tube rope out of the water, and a 4 stroke, or at least a newer design 2 stroke.

Pulling the kids on a tube was great, but so was the wine, cheese and a sunset.

That's my take on it anyway and it sounds like you've got the right mindset. Go with the boat length that works for you and match it up with the appropriate prop for your combination.

I wouldn't go with a 2-stroke on a pontoon boat, btw.

If you're at all close to Tennessee you might check out the Build a Pontoon feature on the Leisure Kraft site to get a feel for pricing. (Looks like about $15,329 for a very nice 24' boat with vinyl floor covering, changing room/sundeck, ski tow, four gates and the rigging to match your engine.)

Other than that just find a manufacturer who will work with you and who can service your existing engine.