Prop keeps blowing out...

[smoedog]

So I think I finally got the issue with my motor blowing out adapter plate seals behind me, now I am dealing with the prop. I've uploaded a picture of where the motor is sitting now and thats as low as it will go. Its a force 50 turning a solas amita 11.6x11 3 blade prop at 5200 RPM and I can get about 18MPH on GPS with me and my wife.

The issue is if I have any weight at all at the front of the boat the prop will blow out and rev up to 5600 rpm and drop of speed. I have to damn near stop the boat before it will grab again. I have marked the prop and hub and nut to see if it was slipping but its not. So where do I go from here. I was trying to find a cheap 4 blade prop around 12.5 inches but the biggest I can find is an 11 inch.

What about throwing a cheap set of hydro foils on there? Not worried about speed just want to be able to have my kids sit up front when they want.

 

[MikDee]

No pix here? Need some of engine height!

 

[smoedog]

No Title

Sorry Forum keeps messing up

 

[MH Hawker]

drop it down lower till it stops blowing out.

 

[Jeep Man]

I don't see how a 4 blade will help.You may have to source an extra long shaft (25") if you can't drop any further. Larger 4 blades are available. I have a 13.75x10 on my Merc., replacing a beat up 14x11. If you do go the 4 blade route,remember to drop by 1p to match the same RPM as before.

 

[Jeffromxer]

I recently have gone through a similar problem with my force 75 on my 20 foot toon. I tried to prop it as my max RPMs were 6000. It had a 12.1x9 3 blade on it. I bought a 11.6x12 3 blade and installed it. My max RPMS were right at 5000 but the prop would blow out with even the slightest boat wake, sharp turn or people in front. I also tried a hydrofoil but it made the problem worse due to the extra stern lift they are designed to produce. I ended up taking the foil off and putting the 9 pitch back on and it cured the problem. I just have to throttle down slightly to my max recommended RPM. I believe the problem is that the 12 pitch prop I got has significantly smaller blades than the 9 pitch. The bigger blades is what defines it as a "pontoon" prop. I have been searching for a pontoon prop for my motor(97 Force 75ELPT)but cant find one. You may have to go down in pitch to get a pontoon prop with larger blades that will bite. For my motor that seems to be anything over a 12" diameter. Anything less than that seems to be for a planing hull boat and has smaller blades.

 

[crb478]

Move all the weight you can to the back of the boat, batteries, gas, anchor, anything that you can. It probably won't be enough, but try that first. Next step will be getting the motor farther back or lower. You can use an offset jack plate to do both. The farther back the motor is the lower it will sit in the water. Right now you are playing a big game of see-saw with the boats balance point. Kids in front lift the back end and take your prop too high to be effective.

 

[MaPaHa]

The 4 blade props help for sure. I use Power Tech props out of Louisiana and they have always helped me select the right prop for the application. They know what they're talking about. I'm running a different motor than yours but they spec'd a 4 blade - big ear Off Shore prop for mine and it works great. I've found that most boat shops don't really know props that well and every time I ask about one I got a different answer. PT can spec it for you but you have to buy it through one of their dealers which isn't hard to find.

 

[ahicks]

<<< I've found that most boat shops don't really know props that well>>>

Amen....