Change propellers?

[JoeTe]

Hello everybody. I had a problem with my propellers (they are broken) and I need to buy a new one. My boat is a 23 ft with volvo penta 5.0gi v8 250hp and duoprop DP-SM 1.95 drive. Actually my boat have a D4 propellers and boat go until 25-30 at 5000rpm (with hull clean). So I would like go for propeller for more speed (although I lost some acceleration) and go cruiser faster with less rpm.
So do you thing could be better go to D3 kit or D5 kit? (Really I don't know so much abouth propellers). I found a D5 kit second hand cheap so if D5 is for more top speed could be good.. but I need help because I don't want to throw money.

Thank you in advance!

 

[alldodge]

Howdy

I would not change a thing, from your numbers it appears you have the optimum setup. If you increase pitch this will reduce your rpms, but in most all cases will not cause you to go faster or save fuel. You want the motor to reach max rpm's at WOT and looks like your does

 

[Sea Rider]

What's the max wot rpm factory stated ? 5 K rpm was achieved while lightly, medium or heavily loaded ? It's much better a faster hole shot than slight more top end speed.

Happy Boating

 

[JoeTe]

Howdy

I would not change a thing, from your numbers it appears you have the optimum setup. If you increase pitch this will reduce your rpms, but in most all cases will not cause you to go faster or save fuel. You want the motor to reach max rpm's at WOT and looks like your does

Thank you for you reply. I'm sure that my setup isn't too bad (or probably is good) but maybe I can modify a little bit for go faster o save fuel. Really I don't know if D5 have more pich or less than D4 but in volvo penta catalogue D5 put for more knots so I guess that yes have more pich. Rear D4 is 4 blades and rear D5 is 3 blades

 

[JoeTe]

What's the max wot rpm factory stated ? 5 K rpm was achieved while lightly, medium or heavily loaded ? It's much better a faster hole shot than slight more top end speed.

Happy Boating

My gauge limit is 6k rpm and volvo penta specs say WOT range is 4800-5000 rpm sometimes if hull is clean, trim good and sea very good I can go until 5500 and 30knots but for example my cruiser speed is about 3800 at 17 knots. Really I don't need a top speed but I would like increase my speed cruiser for fuel save.
Really if finally I have to buy news propeller probably go to sure to D4 again but like I found second hand D5 propellers (50% of new one) maybe is a good chance

 

[alldodge]

The problem I have with VP props is I don't know what pitch a D4 prop is. Without knowing the pitch I'm unable to determine the amount of slip

 

[JoeTe]

The problem I have with VP props is I don't know what pitch a D4 prop is. Without knowing the pitch I'm unable to determine the amount of slip

Yes I don't know why VP don't say pitch. But if you see that catalogue:

http://www.pentamarine.co.th/pdf/propellers.pdf

D5 look always a top speed higher than D4,D3... etc
So I guess that D5 is just a little bit more. What do you thing?

Based in that catalogue if my drive was a single propeller go from to D4 to D5 woulde be like go from 13x15 to 15x15

 

[alldodge]

Yes I don't know why VP don't say pitch. But if you see that catalogue:

http://www.pentamarine.co.th/pdf/propellers.pdf

D5 look always a top speed higher than D4,D3... etc
So I guess that D5 is just a little bit more. What do you thing?

Based in that catalogue if my drive was a single propeller go from to D4 to D5 woulde be like go from 13x15 to 15x15

If (the big IF) the higher pitch prop is turned at the same rpm as the lower pitch prop, then yes the boat will be going faster. The issue is that the motor cannot turn the higher pitch prop at the same rpm as to lower pitch. So in most cases you actually loose top speed with high pitch, and while the rpms will be lower at the same cruise speed, the engine may be burning more fuel because its lugging.

Example: a 15 inch prop should travel 15 inches with one revolution with zero slip.

If I substitute D4 with 15 pitch then your slip is 5.28% which would be great at 30 knots or 34.5 mph
16 pitch the slip comes to 11.2 which is ok but maybe a bit of turning on the prop or trim

If you trim up and rpm increases and also speed increases this is good, but if you trim up and rpm comes up but speed does not increase then you getting slip. IMO best way to find optimum speed and least slip is, bump trim up (ever so slightly) then wait 5-10 seconds and watch speed. Repeat until you find optimum. When throttle is increase to WOT, trimming up more may not be the best bet, you may be better off trimming down a tad.