What is your cruising speed?

[fonsim]

Good morning

I want to know if my 28 is in the numbers. I have twin 350 mercruisers mpi and my cruising speed is 22knots at 3200rpm. How much speed you get?

Thanks

[Leigh]

I have an '85 28 w/ original 350's, 1500 hours. Props are 17x16. 3200rpm gives me 22 knots or so, although I normally cruise at 2950-3000, which is about 20 knots depending on fuel load, seas, etc. At 3200 the secondaries are opening up my 31 yr. old quadrajets. Leigh

[MarkD]

Very much inline with mine. I was running a know or two slower with my old Bluewater 260HP 350's - 18-19 knots at 3000 rpm. My new 315 HP carb'd engines are about 20 knots at 3100.

[makomike1]

I have 1973 B 28 with crusader 270hp .17x18 prop with a #3 cup and it cruises around 20-21 knots. Do any of you have any cup in your wheels? Last year I had prop shop put a # 7 cup in it and I was cruising 22knots at 2900rpm. Nice speed but my wot was only 3900rmp. so this year I had them drop the cup to #3 and my wot is 4300 rpm. Mike Weiss

[Kevin]

I reduced the pitch and increased cup over the years. Started with 17 17 and am now 17 14 progressive pitch with medium cup. Cruising 25 knots 15 gallons hour. Diesel but low horsepower at 212.
New shop in town with scanner computer thing and I'm going to give them a try. I think I am about maxed out at cruise speed potential but going to give technology a chance.

I have learned by listening to the older more seasoned salts that cup is almost always better than pitch. Not sure if that applies to gassers or not.

[fonsim]

I have 1973 B 28 with crusader 270hp .17x18 prop with a #3 cup and it cruises around 20-21 knots. Do any of you have any cup in your wheels? Last year I had prop shop put a # 7 cup in it and I was cruising 22knots at 2900rpm. Nice speed but my wot was only 3900rmp. so this year I had them drop the cup to #3 and my wot is 4300 rpm. Mike Weiss

Sorry for the ignorance but what part is the cup?

[Howesounder]

Cup, when a prop has it, is an extra...."curl" on the trailing edge of the propeller the sort of direct the flow more straight rearward, and allows more forward speed with a propeller, without having the baggage of extra pitch at all rpm. There seems to be a numbering system for how big that curl, or cup on the trailing edge is. I think only planing speed propellers get cup, never on a displacement propeller.......so where a speed boat with a 17x17" prop could not handle any more pitch, or it would not get to full rpm, and might be doing 30 knots wide open at redline, will often perform better with a bit less pitch, but have cup instead.

Steve

[fonsim]

Cup, when a prop has it, is an extra...."curl" on the trailing edge of the propeller the sort of direct the flow more straight rearward, and allows more forward speed with a propeller, without having the baggage of extra pitch at all rpm. There seems to be a numbering system for how big that curl, or cup on the trailing edge is. I think only planing speed propellers get cup, never on a displacement propeller.......so where a speed boat with a 17x17" prop could not handle any more pitch, or it would not get to full rpm, and might be doing 30 knots wide open at redline, will often perform better with a bit less pitch, but have cup instead.

Steve

Thanks for the info.

[scot]

Kevin..

I reduced the pitch and increased cup over the years

That's the correct approach IMHO. The cup adds bit and reduces slippage, I would rather have more cup and less pitch to accomplish what I'm after. Cup is a low end and mid-range thing, i.e. where the boat spend all of it's time.

My last boat was a single inboard so it was cheap to play around with several different wheel set ups. Larger diameter, more cup always wins out at cruise speed. never cared about top speed, because I never used it. My prop guy (who is very good btw) always referred to the cup as light, medium and heavy. He has the prop scan, but I'm not certain about the cup numbering system as he doesn't use a numbering system on his cup work.

[bob lico]

whoa!!!!!!!!!!!! kevin -------progressive pitch!!! and a hell of cup !!!!!!! were or who did you find that information next thing you are going to throw rake into the equation . your friend Bob

[Kevin]

Rake is also something I am going to ask about at the new shop. My last guy could not do it and he has since retired.
My understanding of rake is that adding it will lift the bow? In my case I think that will benefit the boat as the more weight I put in the stern the faster it goes. It may add to the hyena look but at 25 to 30 knots I don't care if it starts to look like a poodle!

[bob lico]

yes it will lift bow however the constant pushing the bow down by the 14 degree down angle of the shaft becomes nolified so it becomes a perfect angle of entry at 28 knots and above cruise speed ,thats the trick to cruising at 26/27 knots in honest 4 foot seas.the exact opposite of tabs!.