BF25 Mounting Height Questions

[North Plains Drifter]

I've read through my manual and it says to mount the motor with the CAV plate 0-2" below the transom, after reading numerous threads here, it is recommended to mount it 0-1" above the tramson. Right now it's mounted right at the transom level. I was wondering if raising it would help as it is sluggish getting on a plane?

 

[Sea Rider]

Re: BF25 Mounting Height Questions

The best engine transom height is the one that lets water flow slightly pass under small upper water defector plate. What's written in owners mamual is only a tech refference, the sweet heigh spot must be reached under trail and height adjustment error. That is with engine sitting in a perpendicular position (manual trimmed) well ballanced boat to ride paralell to water surface at wot.

Tohatsu 20hp w/ 3/4" shim and proper trim - YouTube

Check actual engine height at wot, a spotter must check water flow, then go from there shimming transom to raise height if needed. Sweet spot will give excellent hole shot if propped correctly, sligh higher rpm with minimum tail drag, best top speed with current engine and incredible sharp turns in all water conditions. If wanting boating perfection, this works well with all motor brands, a matter to try it.

Happy Boating

 

[JB]

Re: BF25 Mounting Height Questions

Those 1-2" above/below the transom are starting points, as Sea Rider says. Each boat/load combo will have a sweet spot that is unique to that boat. Most boats will perform okay at the starting point but a lot better when fine tuned.

 

[North Plains Drifter]

Re: BF25 Mounting Height Questions

I watched the video. From what I'm seeing is the the cav plate should be underwater and the next plate up just above the water? My cav plate is right at water level when planing. So I'm guessing the motor should be lowered, or is this the trial and and error part to see whether it performs better up or down.

 

[JB]

Re: BF25 Mounting Height Questions

The trial method also depends on whether you have and use PT&T and/or have a setback. What you seek are best WOT rpm that doesn't allow porpoising or ventilation in hard turns.

BTW, Though most commonly called a cavitation plate, the correct term is anti-ventilation plate.

 

[North Plains Drifter]

Re: BF25 Mounting Height Questions

Thanks all for the feedback!

I have a 16" flat bottom, it is underpowered so I'm trying to get the most out of it I can. No PT&T or setback. These suggestions will help!

 

[Sea Rider]

Re: BF25 Mounting Height Questions

If engine sitting at transom and having antiventilation plate at water level, there won't be much to do as will need to chop transom down a bit to lower engine a few inches for water flow to pass under small upper deflector plate. Is the swivel bracket a sit and bolt through transom or it's the hung type ?

Strange it's underpowered, at that tail height should give lot's of rpm and have aireation issues on choppy seas or at tight turns, probably that engine it's not delivering it's full power. Place an induction tach and check max rpm at wot to see if inside min, max rpm working parameters factory stated.

Happy Boating

 

[North Plains Drifter]

Re: BF25 Mounting Height Questions

Not sure what you mean in the difference on the swivel bracket. Mine hooks over the top of the transom, has the screw clamps and bolted on. I'm not really wanting to chop the transom down quite yet. I know I have to get a tach and check rpm's, just waiting till after Xmas for the extra funds. I'm really hoping it's not propped correctly. I bought the boat used a few months ago so I'm still tinkering with things, it has a nice newer motor, I just think it's a little small for the boat.