Prop Questions

[Ryan23]

OK, now that we have the Spit looking pretty decent, I'm directing my attention at getting this old girl up to speed. I've been reading some of the archived posts so I can educate myself on prop selection. Lots of good info but a couple questions.

- Not much info on twin engined boats, how does that figure into the prop slip calculator? Do you disregard the second engine when calculating slip?

- We didn't get a chance to make any GPS runs last night (forgot the GPS). We'll probably do that on Saturday. We had some relatively calm water on the Chesapeake last night, so I was able to push the sticks forward a bit. She held together fine :hyper: and I was able to wring out 5000 RPM (on these Stewart Warner gauges anyway). Damn, she can drink some gas..lol. Three people were on the boat, just over 1/4 tank of gas. Drives are a pair of trimless Volvo 27x's. No clue whether they are 70's, 75's or even 80's.

- I am also clueless on how we're prop'd. The props read "15 CUP 20 23". Obviously 15 is the diameter but what about the pitch? 20 or 23?. No idea on the manufacturer either. I snapped a few pics of them. Maybe somebody has seen something similar. I'm looking at maybe upgrading to a pair of Sola props.


http://mywebpages.comcast.net/scoobywrx/donzi/prop1.jpg
http://mywebpages.comcast.net/scoobywrx/donzi/prop2.jpg

[Ryan23]

Ryan, I know the steering helmets have been removed on the drives but on the drive where the helmet would attach should be a serial number tag and it will contain the numbers 250 270 or 280 and also a letter a b c d that will tell you the drive ratio
another way to tell is the cavitation plate the 250-270 had a flat cav plate and the exhaust came out of the torque tab area the 280 290 had a thicker cav plate that doubled has the exhaust port, but the lowers are pretty much interchangeable so that might not be the best way to id them
i would start looking for a rh and a lh 22 ultras ;) good luck

The drive serial number on the stbd side is a bit odd. Port is a 280, S/N 2806188B, OK "B" ratio is 1.61, got it. Starboard S/N is 2760917E. Yep, "E". Maybe this is an odd ball E-Drive upper attached to a standard 280 "B" drive lower? From what I've read, they are interchangable. The Cav plates are the exhaust ports, so I'm going with 280.

Ryan