Switch from 3 blade 17" x 17" to 4 blade?

[JAndrewG]

I just posted a sale at Flounder Pounder Marine on props.

If I were to switch to 4 blade from the 3 blade 17" x 17" cupped my 340EC currently has, would 17" x 16" be a good start? I could have the local prop place tweak the pitch from there?

I see that there are a pair of Acme 4 blade props in the above size listed. Anyone ever used these?

 

[osd9]

On my 1998 330DA with 7.4's I went from3 bladed 17 X17 to 4 bladed 17 X 15.25. I wanted to gain a few WOT RPMs from what I had with the 3 bladers. If you go down 1" on pitch and maintain the same cup, you would probably maintain approximately the same WOT.

I would talk with your local prop shop and get their advise. Also, if you are changing prop manufacturers, then that ads another variable into your equation.

 

[JAndrewG]

Thanks for the reply Dominic.

Yeah, I'd seen your post on another thread about going from 3 to 4 blades. It sure seems like a good idea; the prop bites better (less slip), so you'd think it would lift the stern quicker and make the boat run more efficiently overall. A small loss in top speed isn't a concern on a boat like this.

I've always been told that these tunnel hulled Sea Rays need cupped props or they'll cavitate. So your 4 blade props had a cup as well? Or does the extra blade surface of a 4 blade mean a cup is no longer needed?

Thanks again.

 

[osd9]

John:

Yes, my 4 bladers were cupped. I don't remember exactly (all records were lost) but it was a "medium" cup as I recall.

later,

 

[rondds]

i've heard about SRs cavitating in heavy seas (and experienced it), but is that really a function of how many blades there are or purely b/c of prop pockets.

handling around the dock will no doubt be improved with the 4 bladers. everytime my boat is hauled, i marvel at how close my little 3 bladers are to the keel (b/c of fuel tank placement outboard of the engines) personally, i've gotten used to putting one engine in forward and one in reverse and nothing happening for a good 4 seconds! i love a challenge.:wow: