Bentley 200 Cruise Prop question??

[Kitchen363]

So, I need some prop advice. I've got a Bentley 200 Cruise with a 90 mercury 4-stroke.
I got my aluminum 13.75 X 15P prop repaired and have dropped a couple miles an hour and the prop starts to "slip" at 4700 rpms and tops out at 5100 with no change in speed. I'm only hitting around 23 mph

I think before the damage/ repaired prop I could get 5000 rpm and hit 25mph. This was before underskinning too!

Here's the question Is my pitch too high? If I went to a 13P would I actully gain some speed

What's everybody else running? And how many rpms should I safely be turning??

 

[rickdb1boat]

Re: Bentley 200 Cruise Prop question??

Same boat, same motor, run the same prop ( Merc. Black Max 13.75 X 15P) and I hit 28 MPH at 5800 RPM's light load just me onboard. Sometimes repaired props are never the same..

 

[rutcutter]

Re: Bentley 200 Cruise Prop question??

I am going to agree with Rick. It seems that your repaired prop is not working well. I would try a new prop first.

 

[lncoop]

Re: Bentley 200 Cruise Prop question??

Due to all the mitigating factors, rake, blade size, cupping etc. you never really know what will happen until you start experimenting. However, the best guess is if you go to a 13 pitch you'll pick up a couple hundred RPMs and maybe slightly improve your hole shot, especially when loaded, but it seems unlikely to me you'll gain any speed. If you were happy with the prop before the re-work maybe you should look into getting an identical new one (if it's still available). If you liked it you could then keep the re-worked one for a spare. Before you do that though, you should probably speak to the shop and let them know what you're experiencing. Sounds like they have a dissatisfied customer and my guess is they'd want to know.

 

[Kitchen363]

Re: Bentley 200 Cruise Prop question??

Same boat, same motor, run the same prop ( Merc. Black Max 13.75 X 15P) and I hit 28 MPH at 5800 RPM's light load just me onboard. Sometimes repaired props are never the same..

Hey Rick, is yours a stainless or aluminum? Or is That black max prop a pontoon prop? Mine is a quicksilver factory prop.

Here's is me problem, I had my prop fixed over the winter time and guess forgot how it performed Last sumer I hit 28 last year but can't remember my RPM's (even with a chunk missing in one of my blades)

I think I'll be in the market for a new prop this winter

 

[lamac]

Re: Bentley 200 Cruise Prop question??

I have the same motor and run a 15 degree prop and get top end at 29 mph by the gps. Sounds like you lost some in the repair. I tried a 12 degree prop but the rpms would go too high at wot and I lost 8 mph in speed, switched back to my 15 degree prop and all is well.

 

[Kitchen363]

Re: Bentley 200 Cruise Prop question??

I have the same motor and run a 15 degree prop and get top end at 29 mph by the gps. Sounds like you lost some in the repair. I tried a 12 degree prop but the rpms would go too high at wot and I lost 8 mph in speed, switched back to my 15 degree prop and all is well.

Just wondering what kind of rpms are you turning

 

[lncoop]

Re: Bentley 200 Cruise Prop question??

Rule of thumb is 200 additional RPMs for every 1" drop in pitch. I suspect the recommended max for your Merc is 5500, but I don't know for sure. Hopefully you do, but if you don't it should be in your manual. 13.75x15 should be about right for that rig, but if your max is 5500 it sounds like you've got some play room. However, I will tell you I have a 90 horse Merc on a 21' barge. Spec on it is 13.5x15, which is what it had when I bought it. My prescribed max RPMs are 5500. I was getting just under 25 mph (GPS) at 5100, so I gave the 13" pitch a shot and hated it. I did get up to 5500 RPMS, but I didn't get any more speed, in fact I lost a little, and the performance wasn't nearly as smooth. I had the original prop cleaned up and put back on and decided that was the right prop for me.

 

[rickdb1boat]

Re: Bentley 200 Cruise Prop question??

Hey Rick, is yours a stainless or aluminum? Or is That black max prop a pontoon prop? Mine is a quicksilver factory prop.

Mine is a 13.75 X 15P Mercury Black Max. standard aluminum prop. It is not the double cupped pontoon prop. The Quicksilver is the same prop, just renamed. The boat/motor originally came with a 13" pitch installed, but over-reved with a light load, so I swapped it out for the 15 pitch.