PROP SPEED

[BILL ROBB]

I have a folding prop on my O'DAY 30 now. I like it for the increased cruising speed under sail, however, I think I'm losing speed under power. My 15 HP Universal barely moves the boat to 4 1/2 knots under normal conditions. Maxing out the throttle might get me to 5 but that's it. Is this normal? It seems too slow for me.

 

[Joe Barrett]

Prop

What RPM's are you getting and what was your speed before you switched prop's? I put a Martec folder 2 blade on my O'Day 272 and gained a lot sailing but lost .75kts (from 6.2 down to 5.5kts) under power. Your loss seams higher than that. Any black smoke at full throtle? You should be getting another knot out of the prop, what brand?

 

[James rohr]

Bill, we need to talk.

I have 1979 O'day 30,cb version. since your boat isn't in the dir. I could'nt glean too much from your post. I have the yanmar 2Qm15 in mine. the 4.5 to 5.0 knts. you mentioned is way too slow. I'm trying to get mine from 6.5 up to 7.0 which is almost hull spd. under power. Here's what i've found out so far. Mine orig had a 16/10 fixed blade. changed to a martek folding 15/12. there's a later model 30cb in my marina and it has a fixed 15/10 prop. i suspect it has the same engine as yours.there are a lot of questions that need to be answered. 1-whats hp@peak rpm. 2-what gear reduction. 3-has knot meter been calibrated,confirmed by other means such as against loran,gps,known measured dist,no current affect. 4-whats condition of bottom. a dirty bottom can affect boat spd by as much as 1.0knts. I have a very accurate tach on my engine,digital - 0.1%. we check engine rpm against boat speed. this tells us whether we have dirty bottom or dragging some weed. Since we race this WINNABAGO ON WATER we're very observant of these conditions. I have confirmed and re confirmed spds And Que Pasa? has no prob. making 6.5Knts under power. however I know that she'll do 7.0 Since changing to the 15/12 Ive never been able to get it again.At 6.5 i'm turning 2400rpm w/ a 2.14 gear reduction. get back to me via e-mail and maybe we can solve both our problems. I've mailed martek twice and have yet to receive a reply. I quess once they got your money, then the h**l with you. Please put your boat in the directory. Its helpfull to have that info avail. for specific prob.

 

[Rodger Berad]

Folding Props

I think that others have mentioned all the obvious causes of a slow down under power, beyond making the wrong spec choice for one's folding prop. Namely, a dirty bottom, exhaust breathing problems (loosing "omph", which is common), not enough RPMs (for a host of potential reasons). I would definitely check these other issues out, while at the same time verifying the spec on the folder that you now have if you suspect you might not be the right size and/or pitch.Regarding the inherent performance potential of folding props under power, here's my experience: I replaced my 17" 10 pitch with a 14" 13 pitch 2 years ago. I now run under power at a faster pace than before the change. Before the change, I motored at 6 1/2 knots at 3100 RPM. After the change, I motor at 6 1/2 knots at 2700 RPM and see 7 knots if I do 3100 RPM. I've verified before and after readings with my knotmeter and GPS. Note that I wanted to do less RPMs and told Gary Beck at Martec this when he asked during my phone call to ask for some advise. Regarding Martec, this is a quite small private company based in Long Beach that enjoys an outstanding reputation in both the racing and cruising communities here in SoCal. Note that they only make folding and feathering props; in fact, their founder invented the darn things back in the late 60s. To the comment about Martec not replying to after-the-sale emails, I suggest that you just give them a call. (564) 435-4494. I've always found them to be very responsive.Good luck and good sailing,Rodger Beard