HP, RPMs, prop, top speed & broken skeg...

[billyman]

Good morning,

I just registered last night & wish I would have a long time ago. Reading everyone's posts is so informative & interesting. On to my question...

I have a 1995 20' Fisher pontoon w/ a 70hp Force w/ a 12.25x9P prop & I seem to run at 15mph (GPS) @ WOT. My RPMs @ full speed seem to run around 4k (+/- 500), but the manual says they should be between 4750 - 5250. In your experience, what prop should I try switching to to get my RPMs closer to 5250 & hopefully net me a few more MPHs?


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On another note, Saturday night I tried backing my trailer up a steep driveway (it was dark & didn't realize how steep it was until it was too late) & broke my skeg off.




- How necessary is this piece to the performance & manuverability of the craft?
- Based on how much is missing, should I try to get it fixed or buy a skeg protector?

Thank you in advance for any advice or experience you can offer.

[mikeherb]

Man, that's a painful picture.

On your prop. Typically you have a 200 RPM change (approximate) for every inch of pitch you change your prop. It's an inverse relationship so for every inch you decrease your pitch, you should gain 200 RPM at WOT. So I would think a 3-4 inch change should get you near your WOT settings for your motor. But, you're already running a 9P so you might be experiencing something else, like a bad tachometer. Perhaps someone else can add some more on this issue for you.

If you have the piece you tore off your motor I would have someone who knows how to weld to weld that back on and a skeg protector might be a good idea. The skeg provides a bit of rudder for your boat, protects your prop and on some motors the skeg is designed to offset prop torque.

[dockholiday]

Welcome billy

That is painful, pretty much agree with sundeck. Try an find a prop shop near you that rebuilds props, sure they can put you in the right direction prop wise. The skeg is a whole other situation. I would check some prices on a repair or replacing the lower unit but given the age and type of motor it might be a better idea trying to find a good used motor. Mechanical work here runs about 100 an hour so it add up quick once you add the parts in. Good Luck and lets us know how you come out.
doc

[badmoonrising]

Only thing I have to add is that the prop is pretty badly damaged. That can effect performance big time.

[dockholiday]

I just ran across this on iboats
http://www.outboardrepairs.com/topics/001773.html

well here is another (not sure how much existing skeg is needed to use this)
http://shop.keelshield.com/index.php?ma ... ex&cPath=1

[billyman]

Thank you all for your advice, suggestions & condolences.
This is an awesome forum.

[dockholiday]

Thank you all for your advice, suggestions & condolences.
This is an awesome forum.

Good luck to you and let us know how you come out.
doc

[schmir]

I just had my skeg repaired. They told me for aluminum welding they would charge $1 per minute. They ended up charging me $20. Mine was not as bad as yours thought. I would get a new prop that not all chewed up and save that one for your spare. Or file it down to smooth. That might help you out a little. Good luck!