Changing props?

[bogus]

The 17 X 15 props on my 95 330 Sundancer are beyond re-working, and I am looking to change to something different. I hold 4500 WOT with current props, which I think are the originals, and to stay on decent plane, I run about 3300. The guy at the prop shop here in Dubuque, IA said that some options are a 4 blade prop with some additional cupping, going with a 18" prop if there is room in the tunnel. I'm not looking for top speed, but a lower rpm to hold it on plane. (A little more on top wouldn't hurt though!) 454 Mercruisers (310 hp) with Hurth V-drives. We are going to pull the props, and have them scanned to see exactly what we have now and go from there. Any thoughts on possible changes??

 

[nigel]

Well I can't give any advice at all for your boat (not very helpful, I know!) but at the end of last season I changed my standard 21" Vengeance props for a pair of secondhand 21" slightly larger diameter four blade props I found on eBay.. slightly pitted in places but otherwise in decent condition. Seemed very hard to calculate the exact performance I could expect - my primary concern was fuel economy and if it didn't help I could always re-list the props and get my cash back, I figured.

Anyway... the first results have been startling: Acceleration onto the plane is quicker, it runs smoother, feels much more stable and controlled in rough seas, will stay on the plane at lower revs and fuel consumption in MPG terms is improved - its still early days collecting figures but somewhere between a 5% improvement when its flat to 10%+ when its rough, I reckon. All round, I'm most pleased. It sounds different and better too - like its revving faster although its not. Some kind of through-prop effect with 4 blades per rev rather than three maybe..

I've not tried it yet but I expect top-end to be lower.. but I don't care about that. Even if I got the same MPG I'd still now go for four baldes for the other advantages. The boat just feels much more planted in the water than it used to.