25 hp nissan hydrofoil?

drew2237

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Apr 2, 2012
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i have a 1648 jon boat with a 1986 25 horsepower nissan with me and my grandfather in the boat the gps says top end is about 29 but in the winter i use it to duck hunt i normally have 3 people and about another 200 pounds in gear (blind, decoys, stove, ect. ) if i put a hydrofoil on the motor will it increase my top end speed? and i have an hydrofoil off of a 90hp johnson will it work on this motor?
 

Sea Rider

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Sep 20, 2008
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Re: 25 hp nissan hydrofoil?

Hydrofoils does not increase top speed, just makes boat/engine combo plane faster. If larger will slow you bit down, worst if not riding parallel to water surface due to badly trimmed engine or improperly ballanced boat as this will increase leg hydrofoil drag. Hydrofoils comes in different sizes to match engine's HP, so probably a 90 HP is too much size for a 25/30 horse.

Will need to intall an induction Tiny Tach, Hardline type, go for a wot spin ideal on flat no wind water and check max rpm achieved with that combo to check how much you could be under or over proped compared to factory parameters and go from there. Probably could pass that old model to same 30 HP which will better your hole shot and end speed. Usually the extra 5 HP is obtained at wot which is at the end of the throttle grip.

Happy Boating
 

steelespike

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Apr 26, 2002
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19,069
Re: 25 hp nissan hydrofoil?

You did pretty good with some info but you should read the stickys at the top of the prop forum and get the info to us.
Your prop size should be near the vase of the blades or under the prop nut.
 

drew2237

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Apr 2, 2012
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Re: 25 hp nissan hydrofoil?

okay i just wasent sure i was just wondering if that would give me a little more top end speed do you guys know of anything that would do that for me besides another prop
 

Mysticwolf

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Nov 8, 2012
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Re: 25 hp nissan hydrofoil?

Been having a similar problem with my 2005 25HP nissan, I tried everything, hydrofoil, prop, electric trim, nothing seemed to help, 3 weeks ago my trim unit broke, so I took it off to have it repaired, when I mounted it back on, I took 2 pieces of 3/4 marine grade plywood and glued them together, then painted it and put that between the trim unit and the transom, and man, that helped me out more than anything else, before that, I couldnt even get my boat up on plane, now it jumps rite up and goes, my next step is to check WOT and I am changing it to a 30 HP by changing the carb gasket and reset the timing, I just ordered a tach to see what my RPM's are running, and hope to get more power soon, Hope this helps you. I am new at this also.
 

ondarvr

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Apr 6, 2005
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11,527
Re: 25 hp nissan hydrofoil?

Foils allow you to possibly raise the motor higher than without one, this may or may not result in a higher top speed and better performance. If you don't raise the motor the drag from the foil can slow you down or create some handling issues. Most are used incorrectly which results in negative opinions.
 

Sea Rider

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Sep 20, 2008
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12,345
Re: 25 hp nissan hydrofoil?

Tohatsu's Nissans are natural water splashers & tail draggers if not correctly height seated at transom due to it's particular tail shape. Shim height accordingly, ballance well boat, trim engine to be pependicular to water level, pass it to 30 HP, place a tach to check max rpm at full wot, change prop if needed, will experiment wonderful results than before...

Happy Boating
 

steelespike

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Apr 26, 2002
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Re: 25 hp nissan hydrofoil?

okay i just wasent sure i was just wondering if that would give me a little more top end speed do you guys know of anything that would do that for me besides another prop
The antivent plate just above the prop should be even with or slightly above the bottom.
just put a stick on top of the transom to hold up the motor while you tighten the clamps.
A prop change isn't the end of the world.Get us your prop size.I have a feeling a change might help everything.
A new Solas Amita prop is about $65.
 

bigriver79

Seaman
Joined
Mar 24, 2011
Messages
72
Re: 25 hp nissan hydrofoil?

With that boat and motor you will be lucky to break 25mph with all your duck gear and 3 people, even with the perfect prop. Pushing a 1648 with a 25 hp with you and your grandfather @ 29 mph is pretty good. A shorter pitched prop could help but I dont think will you see a ton of improvement.
 

drew2237

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Apr 2, 2012
Messages
15
Re: 25 hp nissan hydrofoil?

well what would be a better size motor for that boat? i got a guy that wants to trade me a 40 mariner for the 25 but im worried that it will be too much motor for that boat
 

steelespike

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Apr 26, 2002
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19,069
Re: 25 hp nissan hydrofoil?

the boat should have a tag with the hp rating. Or look up similar size and weight new jons and check the ratings.
 

drew2237

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Apr 2, 2012
Messages
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Re: 25 hp nissan hydrofoil?

it dosent have a tag because i bought it from a junk yard at home welded the few rivits up and put new wood in the transom so there is no tag anywhere on the boat
 

Sea Rider

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Sep 20, 2008
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Welcome to Iboats,,

Probably will be asked to post your own thread or even be redirected....while that happens. Is water indicator (pee hole) immaculate clean ? poke a wire or red cannula from W40, carb clean sprays back and forth while engine is on. If engine was used on salt waters and not correcctly flushed through the years after use, you certainly have salt layers, salt crust formations blocking water passages. If so, flush engine on a barrel with Salt Away till engine pees better.

Happy Boating
 
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