Better holeshot with same rpm's @ wot...possible?

[tawood]

Hi all,
I have a 19' with a 3.0L mercruiser with a 3 blade, aluminum, 14.25x21 prop. I was wondering if I could find a different prop that would give me a better holeshot for skiing, without changing the 4800 rpm wot I have now. I could care less about top speed.
The reason I ask is that I plan to do alot of skiing this summer with passengers in the boat, but I would also like my wife to be able to take our boat out by herself. If I just changed to a 19" 3 blade, I assume my wot rpms would increase past redline, and I'm not sure I could trust my un-mechanical wife to not toast my motor. I am new to prop theory, so I don't yet know how blade number, etc, affects things.
Thanks in advance,
Tim

 

[steelespike]

Re: Better holeshot with same rpm's @ wot...possible?

There are a couple of thing you could try.
The easiest solution would be a 4 blade prop.
Realize resulting rpm will vary but I believe if you drop an inch in pitch
in a 4 blade it will improve your hole shot. The drop in pitch will help maintain your rpm.as the increase in blades will usually drop wot(wide open throttle) rpm. and speed.
A little more complicated but with a broader affect on performance is trim tabs;powered or passive.Smart Tabs are passive, reasonable easy to install,
effective and have excellent factory support.Improve hole shot,stay on plane with less power,improve ride,and reduce no wake speed wander.

 

[wca_tim]

Re: Better holeshot with same rpm's @ wot...possible?

vented prop!!

can make a HUGE difference. (if you're running through prop exhaust)

the holes in the prop base let exhaust gas out along the leading edge of the propeller at lower speeds inducing cavitation and increasing prop slip in the lower rpm range especially under heavy throttle. it works a lot like a sort of gradual stall converter in a hot rod car and serves the purpose of letting the engine run at higher rpms while you're first taking off giving you more power.

I also love 4 blades and find that the good ones are just as fast on the top end and also do better pulling skiers.

based on your post, a solas titan (not hr) is a bargain and i believe can be had in a 19 pitch. I have a 21 that was great for this when my boat ran fastest with a 23 3 blade.

 

[tawood]

Re: Better holeshot with same rpm's @ wot...possible?

Hmmm, 4 blade sounds interesting...

As for the vented, would I stay at the same size? This might sound bad, but I might have an extra vented prop.... my boat came with an extra brand new prop of the same size as the original (14.25x21). I compared it to the prop currently on the boat, and I noticed the only difference was 3 small holes in the prop "collar", at the front base of each blade. Is this vented?

Tim

 

[steelespike]

Re: Better holeshot with same rpm's @ wot...possible?

Sure sounds like it ,give it a try.Let us know how it works out.

 

[tawood]

Re: Better holeshot with same rpm's @ wot...possible?

Okay, put on the prop with the holes (other than the holes it was a duplicate of the prop I took off, 14.25x21)....performance dropped all the way around. Prop seems to cavitate from a dead start: engine really revs out, and gets real loud when I punch it. I do some fishing and trolling, and trolling at idle speed dropped about 1 mph, as well as ALL cruising speeds dropped 2-4 mph. I usually cruise at 3000 rpm and see 24 mph, but now only see 21 mph, and top speed dropped to 40 mph while rpm's actually increased slightly(not that I care too much about top speed). Soooo, I don't think this prop is going to do it.
I'm gonna try a 4 blade next. I can't use trim tabs because I have too much "stuff" on the back of my boat that gets in the way: swim platform, electric trolling motor mount, and fish finder sender.

Another question: The props I have now have a "hub" of some sort, so does that mean I have to replace my prop with another with a "hub"? I've been looking on Craigslist at props, and it looks like most do not have a hub. If I don't use a hub, what kind of nut/washer do I use to connect the prop?

Thanks again,
Tim

 

[tawood]

Re: Better holeshot with same rpm's @ wot...possible?

Update....
I tried a 4 blade 14.5 x 18...this really did the trick! Boating at my 3000 rpm cruise is down to 20 mph, but wide open throttle is 40 mph at 4800 rpms!!! (rpm right where it should be, yeah!) It seems to pull my kids on the tube much easier now too.

 

[steelespike]

Re: Better holeshot with same rpm's @ wot...possible?

There you go; thanks for getting back.Nice to here a success and adds a little more knowledge to the old brain cells.