20' Pontoon with 75 hp

[jackd1023]

Hello all,

Anyone have any ideas or advice on more speed from a 20' Generation III pontoon boat?

It does not have the "full round tubes" it has round on bottom and continues all the way up to the deck.

It now has a 75 hp Merc, 1995, runs at WOT 5200 rpm, I believe it has a 14 pitch prop. and top speed of a whopping 19 MPH, empty. It seems to get passed by 22'ers with 40 hp.

 

[rickdb1boat]

Re: 20' Pontoon with 75 hp

Sounds like it has U shaped logs. 19 MPH is about right with the 75. RPM's are good too. Although the 14" pitch seems a little steep for the 75, the RPM's say otherwise. Might try a 14" X 13" and see if it stays near the max of 5250 with a normal load onboard. But I doubt you would gain much, if any, speed. Bout the only thing you can do is lower the weight on the boat or increase HP to get better speeds. I have a 90 HP on my 20'er and it does 28-29 "empty"..

 

[jackd1023]

Re: 20' Pontoon with 75 hp

Thanks Rick,

So in other words the "logs" are not good?

 

[trendsetter240]

Re: 20' Pontoon with 75 hp

Hello all,

Anyone have any ideas or advice on more speed from a 20' Generation III pontoon boat?

It does not have the "full round tubes" it has round on bottom and continues all the way up to the deck.

It now has a 75 hp Merc, 1995, runs at WOT 5200 rpm, I believe it has a 14 pitch prop. and top speed of a whopping 19 MPH, empty. It seems to get passed by 22'ers with 40 hp.

I'm not certain of your gear ratio but for discussion's sake, if you had 2.40:1 you have a massive amount of prop slip (.34). My 70hp Evinrude is 2.40:1.

Is your current prop a 4-blade? If not I believe you will benefit from trying a 4-blade prop at a lower pitch, 12 or 13, with a cupped leading edge to provide some bow lift. The RPMs are in the correct range but you should be up around 25mph instead.

 

[Silvertip]

Re: 20' Pontoon with 75 hp

You need to do some checking as there may be several things wrong with this boat. 1) has water made its way into the logs. 2) Is the speed measurement accurate? 3) Is the tach accurate. 4) Since the engine is running at 5200 (if the tach is accurate) that would seem to indicate the engine is running on all cylinders but it may not be making full power. 5) A 14P prop does not sound right for that combination even though the tach says it is. The lower unit gear ratio on that engine is 2.34:1. With 75 HP your boat should go a tad faster. I just checked the Yamaha web site and their performance bulletins show a 20 footer with a 50 HP 2-stroke going 20.1 MPH. With 40+% more HP yours should also be in excess of 20 MPH. Remember though, pontoons require much more power to increase speed significantly so don't expect speeds approaching 30 MPH.

 

[jackd1023]

Re: 20' Pontoon with 75 hp

Thanks for the info, I am not positive of the 14 pitch prop. I am also not so positive on the RPM being correct. I am going to hook up an tach and try that too. We have checked the toons One of the toons had a real small amount of water in it. We replaced the gasket and the drain screw and has been perfect ( no more leaks). THe boat normally stays in the water but we do own a trailer, we even pulled the boat out sent the kid down there with a power washer and cleaned the toons after that we may have reached 19 1/2.......Motor runs great


What is this prop slippage everyone keeps talking about?


I am guessing it is in PROPPING I just would hate to throw money at it and not gain anything. I know the prop was repaced, UGGH, family... They said they put on a Mercry black max that the "dealer" told them was a good match. I just can never remember the boat being much faster. I am wondering if it was "proped" wrong when I got it a few years ago.

 

[tashasdaddy]

Re: 20' Pontoon with 75 hp

i have a 140 on my 20' 37 mph. with just me, 34 with 5 on board, but have to balance load.

 

[Silvertip]

Re: 20' Pontoon with 75 hp

Do not spend money on a prop until you've verified everything else that has been mentioned and that you determine the current prop diameter, pitch, and manufacturer. Prop slippage is expressed in percent and is the difference between the distance a prop would push the boat forward with one revolution vs what it actually does. To understand this better, use the 14P prop you said you have. That prop THEORETICALLY would move forward 14 inches with each revolution if it was operating in a "solid" which water is not. Therefore, if your prop exhibited 20% slip, it would only move forward 11.2 inches. Good slip numbers are in the 10 - 12% range.

 

[steelespike]

Re: 20' Pontoon with 75 hp

19 is certainly in the ball park.I checked a couple one was 19 the other 22.Weight and setup are important Your log width will affect speed as well.
Pontoons do tend to have higher slip numbers.You may want to check that the motor is in excellent tune,that the throttle opens all the way.Careful weight distribution,If no problem with venting(cavitation)you could try raising the motor one hole.Verticle not trim.Won't do much on a pontoon but might help a little.
A 4 blade pontoon prop should help.Carefully adjust the trim.Again may not do much but could improve boat angle might help reduce slip.You can put a skin on the under side of the deck. or add 3rd log these could help signifigantly.

 

[Jeep Man]

Re: 20' Pontoon with 75 hp

Definitely do some checking before spending money. As a comparison, my 20' with a 60 hp 4 stroke does slightly better than yours (19.8 mph), so yours should be doing a little better. I know pontoon boats aren't designed to compete with the "Miss Budweiser", but I hope to do some minor mods in the spring to bring the speed up a little. I'm going to raise the engine one bolt hole and I'm also skinning the bottom of the deck to cut down on the drag.
Check your speed with GPS and check other similiar crafts to see what prop they are running. I've got a Bigfoot and will be using a 14x 11 prop. Good luck.

 

[Silvertip]

Re: 20' Pontoon with 75 hp

A 19P prop on a 75 Merc used to push a pontoon is way too much pitch. 19P is relatively standard pitch for the same engine on a planing hull such as my Alumacraft Navigator 165CS.

 

[steelespike]

Re: 20' Pontoon with 75 hp

A 19P prop on a 75 Merc used to push a pontoon is way too much pitch. 19P is relatively standard pitch for the same engine on a planing hull such as my Alumacraft Navigator 165CS.

The 19 refered to was his speed;he's running a 14" still be a little high probably when all is said and done.

 

[tashasdaddy]

Re: 20' Pontoon with 75 hp

i have a 15 in on my toon.

 

[jackd1023]

Re: 20' Pontoon with 75 hp

Thanks Guys for all the advice.

I think we are going to try RPM first, then check the prop.

I would appreciate some info on "skinning" the bottom.

We have contemplated a third toon because this think likes to "nose dive" when loaded even trimmed all the way up, It does have a horrible seating arrangement.

I just bought this boat back I owned it 4 years ago, really didnt need it but It sure keeps the wife busy while I am on the Chaparral lol.

It really seems "draggy" for lack of a better term, it pops right on plane just kinda weird.

 

[steelespike]

Re: 20' Pontoon with 75 hp

Of course it doesn't truely plane more like pops up to speed.
If it runs really flat that might slow you a little.The seating may be pretty easy to rearrange for better balance. Might even help when empty.
There are some pontoon forums you might find some details on 3rd toon options.
I know there are some fiberglass pods that I think do really well.
If you get the speed up it will save fuel as well as time.

 

[Jeep Man]

Re: 20' Pontoon with 75 hp

Thanks Guys for all the advice.

I think we are going to try RPM first, then check the prop.

I would appreciate some info on "skinning" the bottom.

We have contemplated a third toon because this think likes to "nose dive" when loaded even trimmed all the way up, It does have a horrible seating arrangement.

I just bought this boat back I owned it 4 years ago, really didnt need it but It sure keeps the wife busy while I am on the Chaparral lol.

It really seems "draggy" for lack of a better term, it pops right on plane just kinda weird.

Skinning is plating in the underside with thin aluminium flat stock, covering the ribs.

 

[rickdb1boat]

Re: 20' Pontoon with 75 hp

Like Jeep Man said, it's just aluminum sheeting on the bottom of the crossmembers. Mine is .063 thick 5052 aluminum and the cost was about $450.00 to do my 20'er myself. Before and after pics below..

 

[jackd1023]

Re: 20' Pontoon with 75 hp

Man that looks sweet!! nice job!!

Not sure if that will solve my issues though, I really think that I may look into the third toon. There have been a few times when we have got water on the deck and one time over the front rail......I know it was mis weighted but I was not on it to correct them....

Anyone put a third toon on?

 

[Jeep Man]

Re: 20' Pontoon with 75 hp

Man that looks sweet!! nice job!!

Not sure if that will solve my issues though, I really think that I may look into the third toon. There have been a few times when we have got water on the deck and one time over the front rail......I know it was mis weighted but I was not on it to correct them....

Anyone put a third toon on?

I have to say, I've never seen a 20' tritoon. There is another choice, but I can't recall the proper name for it. I'm sure another member will chime in with it. It's a fibreglas unit that bolts on between the two toons. It provides better bouyancy , speed and manoverability

 

[jackd1023]

Re: 20' Pontoon with 75 hp

I have to say, I've never seen a 20' tritoon. There is another choice, but I can't recall the proper name for it. I'm sure another member will chime in with it. It's a fibreglas unit that bolts on between the two toons. It provides better bouyancy , speed and manoverability

If you could possibly dig up some info, or if someone else could it would be greatly appreciated.