new pontoon boat slower than i thought

[fordsohc46]

i just bought a 89 grumman 20' pontoon boat with a 73 65hp 3cyl engine. top speed at wot is 16mph with 4 people and a cooler. i know this aint a ski boat but i was hoping to tube or knee board behind it. i am not sure how to measure what prop i have and not sure if this is normal as its my 1st pontoon boat. it also seems like it sits in the water too far in back and like it never planes out. i am not even sure if pontoons are supposed to plane out flat. any help would be appreciated.

 

[DJ]

Re: new pontoon boat slower than i thought

Probably overpropped. hard to tell without a tachometer.

In GENERAL, the prop pitch should be somewhere around 12" +/- an inch.

Look at the hub of the prop, if you're lucky, the diameter and pitch are stamped there.

 

[fordsohc46]

Re: new pontoon boat slower than i thought

only numbers on prop are 2707 and 033. does that mean anything.

 

[DJ]

Re: new pontoon boat slower than i thought

Not to me, it may to someone else that jumps in here.

 

[fordsohc46]

Re: new pontoon boat slower than i thought

also the motor looks like it sits really low in the water it is all the way down would it help to move it up. i will pull the nut and washer off the prop tomorrow and see it the right numbers are on the inside.

 

[Tex60]

Re: new pontoon boat slower than i thought

I will tell ya that I have also purchased an older pontoon and in researching mine I noticed that pontoon boats of the that time frame had smaller tubes and it was acceptable for them to sit with the tube more in the water. It will never "plane out" like the new ones will with the larger tubes that sit up on top of the water more. That being said I've got to find a new prop for mine also 50hp and I can run 15mph on my GPS wide open BUT I can pull one of my kids or an adult on a tube and it still runs 15mph my prop is a 10 7/8 X 11

I knew I needed to go up to 11.5 or 12" but not sure what I need to do on the pitch being 11 how big a change do I need to make on that? Maybe someone can go off of that my boat has got a 16' deck but the tubes are aprox 19' long.

 

[lakegeorge]

Re: new pontoon boat slower than i thought

We have a 22ft toon with a 60hp Yamaha and it goes 21mph by GPS I would think yours should go at least that fast.
The prop should have the size on it, sometimes it's hard to find the writing.
If you raise the motor you will get a little more speed.

 

[EGlideRider]

Re: new pontoon boat slower than i thought

With smaller tubes, an older 65 hp motor, and the load you had on the boat, I'm guessing you won't get much more out of her even with a prop change. But as others have said, you can't accurately prop it without a tach.

And no the boat won't plane.

Sitting low in the stern is probably normal but you may want to check for water in the toons.

 

[lncoop]

Re: new pontoon boat slower than i thought

With smaller tubes, an older 65 hp motor, and the load you had on the boat, I'm guessing you won't get much more out of her even with a prop change. But as others have said, you can't accurately prop it without a tach.

And no the boat won't plane.

Sitting low in the stern is probably normal but you may want to check for water in the toons.

Probably an obvious question, but are the toons clean? Toons caked with algae and gunk will really slow you down. That said, it does sound like you're pretty close to top speed. Sorry to say it.

 

[fordsohc46]

Re: new pontoon boat slower than i thought

found correct numbers on inside of hub 13 1/4 X 17. i looked it up on prop tool and that is size i should have i am now wandering if the motor is too low in the water. the plate on foot is 4" below the bottom of the center hull{if thats what u call it?} and the water line on the boat sitting in the water is about 6-8" above that. any ideas? thanks

 

[rickdb1boat]

Re: new pontoon boat slower than i thought

17" pitch prop is way to high. Should be looking in the 11-13 pitch range..

 

[Jeep Man]

Re: new pontoon boat slower than i thought

found correct numbers on inside of hub 13 1/4 X 17. i looked it up on prop tool and that is size i should have i am now wandering if the motor is too low in the water. the plate on foot is 4" below the bottom of the center hull{if thats what u call it?} and the water line on the boat sitting in the water is about 6-8" above that. any ideas? thanks

If the plate your referring to is the anti-cavitation plate, it should be within 1 inch of the bottom of the transom. Motor being too deep can slow you down a little. If it ventilates after raising it 4 inches, drop it 1 hole at a time until right.

 

[DJ]

Re: new pontoon boat slower than i thought

found correct numbers on inside of hub 13 1/4 X 17. i looked it up on prop tool and that is size i should have i am now wandering if the motor is too low in the water. the plate on foot is 4" below the bottom of the center hull{if thats what u call it?} and the water line on the boat sitting in the water is about 6-8" above that. any ideas? thanks

WAY TO HIGH PITCH!

 

[lmuss53]

Re: new pontoon boat slower than i thought

One more vote for WAY too high pitch. My 20 footer with 50 OMC had to have an 11p to get 20 mph and 5500 rpm. I think you will need an 11 or 13, maybe a 15 to get the most out of your engine.

I have found all of the prop calculators to be a little over when they recommend props for pontoons. I alwys get one prop lower than their suggested prop for power and water toys and find I'm about right.

You should get a tach, it is important to know that your motor is running in the recommended WOT range.

 

[lncoop]

Re: new pontoon boat slower than i thought

Cool. Sounds like you have a couple of things to try that might help. By the way, I see you're just 45 minutes up the road. Are you a Greers man?

 

[EasleyLife]

Re: new pontoon boat slower than i thought

I just got a 1993 20' pontoon with a 2001 90hp Mercury 2stroke. It had a 13pitch prop and would max at about 22mph with 6 people...this was at about 5200RPM, but it was able to rev over 6300. I obviously didn't keep it above 5200-5500, but it was clearly underpropped.

I made a bold move (maybe stupid move LOL) and upped to a 17pitch. I think I fouled a plug on the test trip though, because it wouldn't start right, it kept dying (especially when I would give it lots of throttle all at once). These all seemed like telltale signs of an ignition problem. Nonetheless, with all the problems I was having, it would get about 4900RPM with 9 people & two loaded coolers.

Today, I replaced plugs and also put a new fuel filter in it, and now it starts INSTANTLY every time--even better than before I thought I fouled a plug. I have never gotten this instant start out of this engine...only had it about 6 months though. Who knows, they might have been bad before. I also "synced" the carbs as per instrucitons I saw on a previous iBoats thread.

Anyways I'll get it out on the water tomorrow or Friday and test out the big pitch jump. Any ideas on how it might go? (HOPEFULLY yall will have good things to say LOL)

 

[fordsohc46]

Re: new pontoon boat slower than i thought

i moved motor up two notches gonna try to test it this weekend if i get time. i may have a way to check rpm with my friends test light and see how it does. if it is still slow and rpm arent spot on i will buy a 11-13" prop and see how it does. i will keep yall posted thanks for the help.

 

[Outsider]

Re: new pontoon boat slower than i thought

.. it should be within 1 inch of the bottom of the transom.

Well, not really, particularly since there's no 'transom', but that's usually a good place to start. In reality, the motor should be adjusted to have the cav plate just above water level when at speed, just above meaning an inch or two ...