Outboard Performance Question

[crabbait]

Without giving away my suspicion, what do you think the problem is with the following scenario (or, is there no problem).

-Had a new Honda BF225 installed, replacing a Suzuki 140hp (that ran great). With the Suzuki, I could use the engine trim to raise the nose way up in the air without cavitating or porpoising (would eventually...). With the new engine, the engine trim has little effect on the boat attitude (can't crank the nose up). Instead, the engine starts to cavitate before the boat attitude changes much.

-On glassy water, the boat wants to gently porpoise and can't be trimmed to run flat.

-Performance is less than expected (top end).

I have more clues but can anybody give me a hint from what I have said so far?

[jimh]

My guess is the mounting height is off. I don't have an explanation for why they require different heights.

[crabbait]

-The roostertail is very short, even at speed.

[GSD]

Shaft lenghts on the HONDA are 30, 25 or 20 inch.
What is your's?

What was the Suzuki shaft length?

William

[crabbait]

25" and 25"

I am pretty sure they mounted the engine too deep. It is bolted through the top hole, the Suzuki was thru one hole down from the top. The cav plate is equal too or a little lower than the keel (should be even with to 1 1/2" - 2" above the keel.

Easy to find out....

[EZLoader]

There was a guy on another forum with a similar problem of cavitating and porpoising. He was told to raise up his motor to fix this. He raised it up up 1 3/4".

His Result...

"Went out today..Didnt catch a thing but was the best day..For the first time my boat ran perfect no cavitation no porposing.Just ran hard at all levels..felt great. Did notice that my rpms had droped from 55-56k to 51k today I have a 13 1/4 * 17 prop that I try next time to get rpms up.. But man it ran like a champ..Trimmed out top speed of 35.2 gps. Now the operating range listed on the motor is between 4500-5500k. Thanks a bunch I cant believe how much diference 1 3/4 inch makes."

[Good News Tuna]

Just went out and looked at mine. Similar boat-same motor. My cav plate is about 2" above the keel. I have used it for two years and I think it needs to come down one hole. Its 22' Wooldrige with a offshore and it cavitates in short seas if its not trimmed way down. Runs good (more cofortable) when trimed down but drive the bow down a bit. Your boats a little heavyer than mine and I would think you could easyly be at that 1.5 - 2" area.

[R Jackson]

Could it be the weight difference between the two motors? :shrug:

[Tacklebuster]

On glassy water, the boat wants to gently porpoise and can't be trimmed to run flat



Does this mean it wants to bounce when you start to trim the motor up or just bounces regardless if your motor is down or is trimmed up? Do you have any trim tabs? The motor location is also a huge factor. Where is your Honda located on your bracket? Just being in the wrong bolt hole can make all the difference in the world.


-Performance is less than expected (top end).




What is your WOT at top end? That there is the tale of the tape. Being able to trim your motor will greatly affect this as you know. If your can not turn the RPM's close to your max, you need to swap out your prop.

[Gundog]

When I first took delivery of my boat I had these same problems the fix was a different prop. I tried lowering my motor prior to changing props and it got worse. From my experience with my boat I would try raising the motor and if that does not work maybe a prop change.
GD

[crabbait]

Does this mean it wants to bounce when you start to trim the motor up or just bounces regardless if your motor is down or is trimmed up?


It want to gently porpoise regardless of engine trim position


Do you have any trim tabs?


Yes, but it should run out flat without the tabs being used.


The motor location is also a huge factor. Where is your Honda located on your bracket? Just being in the wrong bolt hole can make all the difference in the world.


The engine is in the top hole (lowest position). The Suzuki was one hole shallower.


What is your WOT at top end? That there is the tale of the tape. Being able to trim your motor will greatly affect this as you know. If your can not turn the RPM's close to your max, you need to swap out your prop.



Prop is a 19-pitch. Roy has the same boat and motor and is running a 21 pitch. With the engine mounted as deep as it is, the boat does not trim nose-up like it should, Instead, it starts to cav and porpoise as you trim up.

I am sure the engine is mounted to deep. I think the cav plate is at or below the keel height.

[Bait O' Eggs]

I have the same boat and same motor, I am one hole higher than Crabby, though it all depends on if the holes in the boat are at the same location if the motor needs to be in the same bolt holes. :shrug:

I suspect your motor is to low on crabbys boat. I get none of that porpoising thing. :noway:

I am over propped with the 21 pitch, guessed on the conservative side because I didnt want to over rev the motor when I bought the first prop. I can get a tad over 5000 rpm and should be getting closer to 6000, of course if I tilt the motor up high enough I can get as many rpms as I want :wink: Still need to find a bargain on a 19 pitch left hand prop.

[foxer]

I have been told that on boats with an offshore bracket, the cavitation plate should be slightly higher than the bottom of the hull.

[fish Addict80]

If the two motors were the same shaft lengths like you said they should be mounted in the exact sam holes (on the boat and on tthe motor) as before. I did the swap myself when I repowered and matched it all up exactly and it worked perfect.

Also my bracket puts the motor a little over 2 feet from the bottom end of my boat and the motors cavitation plate is almost 4 inches up from even with the keel.

Even with this setup the best position for the motor when running is 3/4 up on the trim.

I think the boat doc said the farther away from the back of the bottom of the boat the higher the engine should be.

It sounds like the height should solve all of you problems. Once you get all that lower unit out of the water and reduce the drag the boat should go pretty good.

Good luck

Luke

[crabbait]

That is exactly what I am thinking. The girl just needs to get out of her own way.

[Starfish]

Sure sounds like you need to raise the motor a bunch, plus make sure you're running a good high-rake stainless prop with a lot of cupping. Not all props are designed to give a lot of lift on a heavy boat. I really like my Tempest Plus, lots of lift and it stays hooked up really well. It sounds like you would want a 19P.