Changing Props - 3 Blade Stainless (LH & RH) to 4 Blade Aluminum props

[hckrphil]

My Boat: 2000 Wellcraft Martinique 3000 (30ft cruiser)

I currently have twin volvo penta 5.7GS motors with Volvo Cobra SX outdrives. I have stainless 3 blade props (one left hand one right hand).... 14-3/4" x 19".

Current WOT is at about 4100ish RPMs.

I'd like to consider changing to ALUMINUM 4 blade props (LH & RH). Boating with stainless props makes me nervous where I boat......

Possibly bump up my RPMs a little (not much).

Thoughts about what size Aluminum 4 blade props I should be looking at?

Thank you!
Phil

 

[wrench 3]

When I changed from a three blade to a four blade my prop shop advised me to drop down one pitch. I changed from a 19 pitch to a 17 and it worked out really good.

 

[hckrphil]

Do you think switching from Stainless to Aluminum will have any major affect?

 

[hckrphil]

I found a few 14.5" x 17 4 blade props.... that would mean i'm decreasing diameter by .25".....

 

[wrench 3]

Between aluminum and stainless I was told that there wasn't much difference in performance unless your running above 300HP.
I'm not sure on the diameter.

 

[hckrphil]

Hmmmm, I emailed Solas... will be interesting to see what they say about their props

 

[wrench 3]

Hmmmm, I emailed Solas... will be interesting to see what they say about their props

I'd be interested in finding out.

 

[hckrphil]

Part #8613-145-17 and 8614-145-17 right here on iBoats..... good price too. I'll wait to hear back from Solas

 

[jimmbo]

You are quite a ways below the recommended WOT range which is 4400 - 4800 rpm. Using 3 blades you will need to drop about 3 or 4 inches in pitch, With a forth blade even more

 

[Senior B]

Concur with above about MAX RPM and you're a bit low. Craft is probably a bit sluggish getting on plane. With the above information I would advise you to get 15 pitch 4 blade props. I

 

[hckrphil]

Def. sluggish getting up on plane.... I have to throw the trim tabs all the way down to get it to pop up... I'll go with the 14.75x15 4 blade prop.

Thanks everyone!
Phil

 

[QBhoy]

As said, you are way off the mark as it is. 4400-4800 is where you want to be, preferably at the higher end, when having your usual trim, canopy up or down etc.
Is the hull clean ?
If all the above is happy and you are still at 4100 wot, you defo need to come down a few inches in pitch.
I know of a few friends (with similar set ups) that run the big 16x16 props with happy results. Never going to be a record breaker but very happy everywhere else and very useable. Especially good at accelerating out the hole.
Like most will tell you, best to try out lots of props to see what suits you best.
All the best.