Hydrofoil for pontoon?

tywiesz

Cadet
Joined
Dec 28, 2022
Messages
23
hi,
new to the pontoon boats so learning as I go and not going too good.
1. pontoon 7m with honda 4stroke 90hp. Motor is trimmed all the way down, if up even a bit the prop just loses its grip.
2. when I bought it it didn't go pass 4800 rpm's than just cavitation and lose of speed
3. advised to do "lips" on this 4 blades, aluminum 14" prop.
4. 160 dollars latter improvement noticed , I could push to 5800 rpms with better acceleration and overall speed reaching 13.5 knots. Still some throttle left to WOT.
5.Meanwhile checked the hub, all good and tried 13" pith 3 blades stainless steel prop, worse performance.
6. advised by the prop shop to try a hydrofoil, got it installed and happy not happy arrived.
Happy coz if not going against the current I can WOT 5850 rpms without any cavitation. Happy coz the turns are so much better at higher speeds. Acceleration better with the nose nice going up at the begining.
Happy as the boat seems to have more stable behavior. In general I guess should not complain as there is a lot of improvement but...
1. lost 1.5 knots speed at WOT.
2. the nose seems dive in, never lifted after initial acceleration.
3. trim the motor up does not do nothing but losing speed
I'm thinking and it would be awesome if somebody has done it and shares their experiance that the hydofoil is too big of a surface. I thought to cut 1" along of it and see if the drag decreases nose goes up? Maybe?
The majority of the seating is on the front so ppl will seat there and that magnetifies the nose dive in too much, with 2 ppl not too much of a problem
I measured how deep the hydofoil is to the surface, 25 cm (10 inch?)
From my photos it seems that the outboard pod is a lot higher than the leg ventilation plate but don't have any measurement of it.
Guy, all your thought highly appreciated and happy new 2023 year.
cheers
T
 

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Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
49,574
Start with lowering your motor, or add weight. Motor height on a pontoon is critical
 

tywiesz

Cadet
Joined
Dec 28, 2022
Messages
23
yes, good advise, can't lower the motor any more coz engine mounting is sitting on the transom already. I'll double check it again. I could add 100kg and see what happens....
 

tywiesz

Cadet
Joined
Dec 28, 2022
Messages
23
Hi,
love the performance after installation but lost some speed at WOT and the boat nose is just not rising properly. I trim the outboard down or up, will not change the nose position at all so I thought too much of the hydrofoil ? 7m Pontoon boat with 90hp 4 stroke
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,342
I’m of the opinion that these things shouldn’t be fitted at all. Any issues they are trying to solve, can be overcome with the proper outboard set up in the first place. Add in the risk of snapping the av plate off the motor…and it’s even more of a bad idea to have fitted. My thoughts.
 

tywiesz

Cadet
Joined
Dec 28, 2022
Messages
23
I’m of the opinion that these things shouldn’t be fitted at all. Any issues they are trying to solve, can be overcome with the proper outboard set up in the first place. Add in the risk of snapping the av plate off the motor…and it’s even more of a bad idea to have fitted. My thoughts.
Hi,
all thoughts appreciated.
cheers
T
 

jlh3rd

Chief Petty Officer
Joined
Jul 10, 2017
Messages
560
that's a wooden transom?....so this pontoon is a homemade one?
How big are the toons?
practically all of the commercial pontoon boats are equipped with "long shaft" motors so that the prop has minimal cavitation/ventilation issues due to the prop being deeper.
All of you're descriptions and attempted fixes point to the prop not being low enough in the water. Pontoon boats, especially older ones, can have these issues.......I speak from experience...
I have a 24' '06 lowe pontoon that I re-powered with a new merc 115 hp.
I had to lower the motor all the way down as the initial setup resulted in cavitation/ventilation issues and couldn't trim up hardly at all....
Dropping the motor the additional 1.5-2 inches made all the difference in the world..........so....unfortunately, you might be the best you're gonna get....

also, I read and posted on your rpm issue.......you gotta be sure the engine rpm is accurate......
you're kinda bouncing around all over.......
Be sure one problem is fixed before throwing other "fixes" in the mix...
As a comparison....my pontoon gets about 24 mph at 6000 rpm...

also, I've read multiple reports on hydrofoils and they can help but all reports say top speed will suffer some.......I also agree with the experienced guys on here in that it might, repeat might, cause more issues than it fixes.........It would be a last resort for me if I had exhausted all proper fixes......once again, fix one problem at a time....
 
Last edited:

tywiesz

Cadet
Joined
Dec 28, 2022
Messages
23
Hi,
you are v.right, pontoons 6.5m aluminium and big motor pod underneath. Short shaft it seems to be the problem. I have one hole to go down on the motor bracket but it is seating on the the transom already. And yes I'm bouncing from one issue to another, hahah. Maybe buy 30 doll, electronic tacho which wires to the spark plug h.volt.wire and compare.
cheers
t
 

jlh3rd

Chief Petty Officer
Joined
Jul 10, 2017
Messages
560
lol...just trying to help....I went through 4 props when propping my pontoon with the new motor....and I kinda knew what I was doing....it's a boat...
 

tywiesz

Cadet
Joined
Dec 28, 2022
Messages
23
lol...just trying to help....I went through 4 props when propping my pontoon with the new motor....and I kinda knew what I was doing....it's a boat...
your help appreciated no question on that. Don;t have proper resources to replace my motor, hahha, grrr. It is what it is sort of reality.
I got what paid for hahhah. To my ear idle is set too high gona lower it and verify my current meter with another one. I may just coil a bit of wire on h.volt of one spark plug and connect frequency meter than multiply x4 as got 4 cyl.motor, right? Fix the rpm first
cheers
T
 

jlh3rd

Chief Petty Officer
Joined
Jul 10, 2017
Messages
560
honda might have a long shaft conversion kit for your motor....
 
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