MICRO SKIFF !! Cavatation? 25hp Yamha

3915 Views 16 Replies 8 Participants Last post by Tailwaters, Oct 22, 2019

JonathanJ813

Discussion Starter · Oct 19, 2019

9

I just got done building my micro skiff

2019 Mangrove Bay IBIS ..
Its basically a 16 dorado mold

Ita powered by 2019 Yamaha F25 stock aluminum prop is 11.25 with my stock prop the boat would not get up to speed it would cap
At 8mph with me and my wife on boat I weigh 235 and she is about 130

So I changed my propeller to a 13 prop from 11.25 since going up to 12 didnt seam much of difference and now she does 29mph with just me and 25ish with a passenger but some times with a passenger I cavitate, i believe ? Some times it take time to get on plane and on sharp turn we lose our momentum and go into cavatation

So my questions are ! Am I to high above water ?
Should I change my prop ? Should I add wings lol. Idk what to do I was also told maybe I should cup my propeller would that help talk to me guys I'm in a pickle

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manny2376

· #2 · Oct 19, 2019

JonathanJ813 said:
I just got done building my micro skiff

2019 Mangrove Bay IBIS ..
Its basically a 16 dorado mold

Ita powered by 2019 Yamaha F25 stock aluminum prop is 11.25 with my stock prop the boat would not get up to speed it would cap
At 8mph with me and my wife on boat I weigh 235 and she is about 130

So I changed my propeller to a 13 prop from 11.25 since going up to 12 didnt seam much of difference and now she does 29mph with just me and 25ish with a passenger but some times with a passenger I cavitate, i believe ? Some times it take time to get on plane and on sharp turn we lose our momentum and go into cavatation

So my questions are ! Am I to high above water ?
Should I change my prop ? Should I add wings lol. Idk what to do I was also told maybe I should cup my propeller would that help talk to me guys I'm in a pickle

when you say you went from an 11 to a 13, you’re referring to your propeller’s pitch? Seems really odd that you went from 8mph to almost 30mph.

also, what RPM were your turning with each prop?

JonathanJ813

Discussion Starter · #3 · Oct 19, 2019

manny2376 said:
when you say you went from an 11 to a 13, you’re referring to your propeller’s pitch? Seems really odd that you went from 8mph to almost 30mph.

also, what RPM were your turning with each prop?

I dont have rpm gauge and yes I went from 111.25 1 to 13 pitch

richg99

· #4 · Oct 19, 2019

Cavitating with a passenger (and not without one) sounds like the passenger is forward, and the stern is lifting due to the weight being up there. Is that a possibility?

Backcountry 16

· #5 · Oct 19, 2019

Need trim tabs or a cavitation plate on your motor to push the front down trim tabs are very important for a microskiff in my opinion.

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Smackdaddy53

· #6 · Oct 19, 2019

Backcountry 16 said:
Need trim tabs or a cavitation plate on your motor to push the front down trim tabs are very important for a microskiff in my opinion.

Trim tabs and compression plate (cavitation plates aren’t really anything other than hydrofoils, compression plates turn down on the sides and hold water around the prop) are definitely huge assets if you want to maximize performance on just about any boat.
It looks like your motor is actually lower than it should be. The bottom cavitation plate on the lower unit should be even with or a little above the bottom of the hull with the motor trimmed flat. Take a straightedge and hold it on the bottom of the hull and trim the motor flat and take a photo for us.
As far as going from 8mph to 25mph that’s odd...but if anything I’d probably look at a stainless prop with a little cup. Talk to a custom prop shop to get you dialed in if you don’t want to be playing “pin the shelf prop on the motor” repeatedly.

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manny2376

· #7 · Oct 19, 2019

JonathanJ813 said:
I dont have rpm gauge and yes I went from 111.25 1 to 13 pitch

a few thoughts:

You’re going to need to know what RPM you’re turning to tune your prop. Look for a “tiny tach” on amazon. Easy to install and will get you the numbers you need.

You’re going to need to know how many RPM your motor turns at wide open throttle. Should be in your manual, or check google.

Now, with those numbers in hand you can tune. You want to be in your sweet spot for RPM at WOT. That means your pitch is correct. Onto the blowout issue... if you’re blowing out on turns, you can A: adjust your motor height (see cav plate comment above and get a level). B: small skiffs are weight sensitive, move the load around a bit. C: you can try a 4 blade prop or add some cupping to your current prop. Also, look into a stainless prop for your application. Give Barracuda Performance Props a call. They’re by the Falls, across from Eric’s outboards. I would start there before adding a compression plate or wing. Also, I would highly recommend trim tabs. I think all small skiffs really benefit tabs and the ability to really adjust the attitude of the hull. Good luck!

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manny2376

· #8 · Oct 19, 2019

@JonathanJ813 disregard my south Florida prop shop recommendation. For some reason I thought you were in miami. Give Ken at propgods a call. He knows his stuff!

Reactions: 1

el9surf

· #9 · Oct 19, 2019

Why not just talk to the builder? They should have the setup dialed in better than anyone else.

Reactions: 1

Smackdaddy53

· #10 · Oct 19, 2019

el9surf said:
Why not just talk to the builder? They should have the setup dialed in better than anyone else.

Not always the case, even with “top tier” builders. It’s worth a shot though.

JonathanJ813

Discussion Starter · #11 · Oct 19, 2019

Smackdaddy53 said:
Trim tabs and compression plate (cavitation plates aren’t really anything other than hydrofoils, compression plates turn down on the sides and hold water around the prop) are definitely huge assets if you want to maximize performance on just about any boat.
It looks like your motor is actually lower than it should be. The bottom cavitation plate on the lower unit should be even with or a little above the bottom of the hull with the motor trimmed flat. Take a straightedge and hold it on the bottom of the hull and trim the motor flat and take a photo for us.
As far as going from 8mph to 25mph that’s odd...but if anything I’d probably look at a stainless prop with a little cup. Talk to a custom prop shop to get you dialed in if you don’t want to be playing “pin the shelf prop on the motor” repeatedly.

Thanks bud good input

Reactions: 1

JonathanJ813

Discussion Starter · #12 · Oct 19, 2019

richg99 said:
Cavitating with a passenger (and not without one) sounds like the passenger is forward, and the stern is lifting due to the weight being up there. Is that a possibility?

Yes I agree

JonathanJ813

Discussion Starter · #13 · Oct 19, 2019

el9surf said:
Why not just talk to the builder? They should have the setup dialed in better than anyone else.

Yea I mean abe was very helpful at mangrove bay but my combo is diffrent then some he built before most of his set ups are tiller motors tohatsu or Suzuki with diffrent weight horsepower I guess I'm special lol

Reactions: 1

jay.bush1434

· #14 · Oct 21, 2019

As said above, compression plate and some cup on the prop. To get the best performance from your prop, you will need to know engine rpm and boat speed.

Reactions: 2

Tailwaters

· #15 · Oct 21, 2019

I had a stock aluminum Yamaha prop on my 25hp 2 stroke. It had a bad problem with cavitation, mainly in turns. I switched props and the problem went away. Still have an aluminum prop at the same pitch but went with a different manufacture. It's amazing the difference in performance.

Reactions: 1

JonathanJ813

Discussion Starter · #16 · Oct 21, 2019

Tailwaters said:
I had a stock aluminum Yamaha prop on my 25hp 2 stroke. It had a bad problem with cavitation, mainly in turns. I switched props and the problem went away. Still have an aluminum prop at the same pitch but went with a different manufacture. It's amazing the difference in performance.

What manufacture did u go with

Tailwaters

· #17 · Oct 22, 2019

It's a 3 blade aluminum Solas prop. I had to have a compression plate with the Yamaha prop. to pervert it from cavitating and it still happened from time to time. After hitting a rock I replaced it with a 4 blade Solas and took the compression plate off to see how it would run. Ran perfect and no cavitation. After hitting another rock my local marine supply store only had a 3 blade. Since they are relatively inexpensive I got it figuring I'd order another one later but didn't need to. The Solas 3 blade worked great too. I get 24-26 mph which is plenty fast enough for what I do.

On a side note I stick with aluminum props on my creek boat due to all the rocks in the area I fish. I had to replace a couple drive shafts on my old creek boat. I'd rather replace a $80 prop and be able to limp back to the landing than break a $400 drive shaft and have to be towed in. If you don't have to worry about rocks go with SS.

I also noticed a huge difference in performance with different props on my offshore boats too. finding the right one can make all the difference.

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