Prop to reduce transom lift?

[Bluejinx202]

hi all, I have a 65mph 15’ centremount 6cyl wooden boat. I can’t get the hull to sit still at full speed. It start leaping out of the water around 60mph and continues to gain speed but I’m worried it’ll end with a roll over. Is a propellor capable of changing this? I can change the front lift or attitude with cab plate and I’ve tried longer and shorter shafts. I use an 11x12 with minor rake.

 

[hallett21]

2 blade or 3 blade?

Are you saying the Cav plate does help or doesn’t?

 

[ONE-A-DAY]

What type of prop, post a picture of it.

 

[Bluejinx202]

It’s a 3 blade

 

[Bluejinx202]

The cav plate does change it. It seems to elevate the front and change the overall angle of the hull. When I lift it too high it feels like it drive up out of the water and when runs out of hull it crashes down and lands on its belly.

The only way to make it stop lifting is do run the plate with the trailing edge under the boat which will hold it reasonably steady but will be down on mph

 

[Bluejinx202]

Is the prop blade shape to blame for this? Would less rake possibly sort this out?

 

[hallett21]

I’m thinking that you need to try a 2 blade.

Do you know your strut angle?

I’m not a Vdrive expert by any means but sounds like you need to get your thrust going “flatter”.

You could also be running out of hull at that speed.

 

[Bluejinx202]

Strut angle is 10.8deg

It’s a centremount so to get that I had to dry sump the engine and mount mount it so low the main caps nearly touch the floor and the block is nearly in the front seat

 

[hallett21]

@AzGeo

AZ is very knowledgeable in rigging etc hopefully he can chime in

 

[hallett21]

Sounds like you should try a 2 blade

 

[jstnoc]

That looks like a ton of prop for that small of a boat. Let the pros chime in but it looks like a smaller prop / 2 blade will help for higher speeds.


Sent from my iPhone using Tapatalk

 

[vdcruiser]

A lot of unknowns here, since this is not a V drive and the hull is a unknown quantity. I agree that you should try a 2 blade, maybe 10 3/4 dia x 15 pitch. Might be a little hard to find a used one since it is a right hand rotation. Also be careful turning your prop 5000 rpm or more since it appears to be bronze. Do I see a bend in the cav plate right below the cav plate control rod. If so, that would make it hard to bend the plate. Neat looking boat, would be nice to get it ironed out. Some of the cracker box guys might have something.

 

[Bluejinx202]

A lot of unknowns here, since this is not a V drive and the hull is a unknown quantity. I agree that you should try a 2 blade, maybe 10 3/4 dia x 15 pitch. Might be a little hard to find a used one since it is a right hand rotation. Also be careful turning your prop 5000 rpm or more since it appears to be bronze. Do I see a bend in the cav plate right below the cav plate control rod. If so, that would make it hard to bend the plate. Neat looking boat, would be nice to get it ironed out. Some of the cracker box guys might have something.

I turn the engine/prop to 6800 so not ideal for a brass prop I suppose.

No breaks in the cav, it’s a cut out I think you are probably seeing in the pic, there was a thought that maybe let the rooster off the prop not hit the cav but wanted the stability of the big plate.
I have never tried a two blade prop, I’ve heard they shake so hard it feels like the strut is going to come off?

 

[toyaddiction]

I just want to see more pictures of the boat. That thing looks cool. We all want to go faster but 60 seems like your hauling ass. Mine is 18 feet, does 45 and needs more prop. I am happy with that as I am afraid it might fall apart if it goes any faster.

 

[vdcruiser]

With the new picture, I can see why I thought it had a break in it. Two blades do tend to vibrate at take off and slower speeds, but are smooth at higher speeds. The newest Menkens I have on my 21' Howard is pretty smooth all the way around.

 

[aaronschiada]

you dont need a 2 blade. send your prop out and tell them you have way too much bow lift. they should be able to tweak your 3 blade. if not, then they may need to redesign you a whole new prop. your application isnt exactly common, so throwing any ol 3 blade on there aint gonna do the trick. are you getting the RPM out of this prop that you want? there are so many other reasons why its chining like that...but those arent cheap fixes...

 

[aaronschiada]

didnt see that it was a bronze prop. buy a new one. cool boat btw!

 

[Bluejinx202]

Any recommendations for a manafacturer to buy a new prop? I need around an 11x12 right hand.

 

[Taboma]

Any recommendations for a manafacturer to buy a new prop? I need around an 11x12 right hand.

I posted over in your restoration thread, again, very cool boat.
I'd think with the popularity and history of the Seacraft in Aus., for various racing venues, isn't there a user's group or any old timers hanging out at boat shows or ski racing events ? I bet somebody has a garage full of stuff they've kept forever and are looking for a good home. I'd expect some of these ole birds to be extremely welcoming to new Seacraft blood.
I think it's cool you're on RDP sharing this project, but from what I can see of your rebuild thread, this is a very unique boat which will present unique problems and solutions. Good luck !!

 

[aaronschiada]

Any recommendations for a manafacturer to buy a new prop? I need around an 11x12 right hand.

Bergeron Marine, Valley Prop, Menkens

 

[fastenuff3]

View attachment 632007 hi all, I have a 65mph 15’ centremount 6cyl wooden boat. I can’t get the hull to sit still at full speed. It start leaping out of the water around 60mph and continues to gain speed but I’m worried it’ll end with a roll over. Is a propellor capable of changing this? I can change the front lift or attitude with cab plate and I’ve tried longer and shorter shafts. I use an 11x12 with minor rake.

you need to move prop back. it will pick the tail up. the prop is to far under boat driving the boat out of the water.you can ad a lot of horsepower and it will drive nose over.

 

[Jimmy]

Should try Steve Evans hes up in QLD. Hes the only guy in Oz that gave me a straight answer.

Nice looking boat too.