Another prop question: 20' MA advice?

[gofastsandman]

http://www.classicseacraft.com/commu...t=prop+testing

The dia. and pitch were all over the place, but I learned a lot of subjective intel.

Thx, BW.
Cheers,
GFS

[76Red18]

rkarran I would say too much prop. I run an old style sst 15 x 15 most of the time on my 18 with a 150 about like yours. 39 - 41mph @ 5400 trimmed with a heavy load. Planes very easy and runs well when it gets a little rough.

Sounds like your motor is well tuned. You ever check compression? Mine is 103 - 106 with about 300 hours.

[rkarran]

Red, my compression is right about 95, across the board. Was told this is a low-compression model by design.
Yes, I'd like to try a 15 x 15.

[gofastsandman]

They made about 11 versions of this motor. Low compression motors will generally last longer. They made 90 commercial motors and 130 bass boat gt`s. They matched the slugs side for side, The key is each bank should be close. 5-10% is considered normal. I`m 87-92 cold, carbs closed. That is a bargaining tool right there.

Cheers,
GFS

[rkarran]

I recorded some numbers this morning. Decarbing the motor did not make any difference to my max rpms.
1500 rpm 5.7mph
2000 rpm 7.7
3000 22.8
3500 27.7
4400wot 34.9

I think I need to try a 15 x 15 prop.