ben2go
Guru
The engine turns 2.03 times to make the prop turn round one time, 2.03:1. This gives a bit more torque to the prop but reduces prop speed. IIRC.
Hendo's Randall 35 Cray Boat complete rebuild, Perth, Western Australia
- Thread starter Hendo78
- Start date
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OldDan1943
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Did you clean up the lot where you worked on the boat?
You on patrol? :lol:
ben2go
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Nomad Willy
Guru
More prop clearance would be a good reason indeed. And Matts boat may be shorton clearance. But I’d advise him to run the numbers first.
And a blade area increase would lower prop loading and probably cavitation problems ... if they exist. But unless the prop is heavily loaded cavitation is unlikely.
But if blade area is good a three blade prop is better.
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Hey mate.
By clearance you’re referring to the distance from blade to hull yeah? and run the numbers as in the calculator or actually doing her shakedown sea trial?
How will I know if the three blade is enough or if it’s cavitating. My ski boat cavitation but that was at 70knots and I could here it slip and feel it. I’ve been told to expect 8-10 knots so won’t it be had to feel it drop off or is it the same sensation as I had felt in the ski boat?
The first two pics are what I have and the third pic is what the manufacturer of my current screw suggests I get in the same size diameter. Essentially just adding a blade. Would I benefit from it enough to justify the $2600
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Nomad Willy
Guru
Matt,
Depends on the hp loading.
The picture in the link shows a max blade area 4 blade. Probably unsuitable. I suspect you don’t have the power to be needing that. A 3 blade version of that 4 blade shown would probably be better. But a 4 blade with smaller blade area could work too. But not needed if a 3 blade has enough blade area. You only need a 4 blade if the 3 blade has insufficient blade area.
Have you posted your hp/rpm, gear ratio and available clearance here on TF? There’s several with books and other info that can/could come close. You might find a used prop to test. Only about 2” of change can be made so it’s good to come as close as possible before buying a prop.
And FYI I’d steer clear of cupped blades and overpropping. Choose a prop that alows your engine to sing rather than labor.
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If that's the case then I may not need an additional blade as i am currently running the 3 blade version of that 4 blade in the pic. The 4 blade is what austral said I could fit. What is the benefit of that extra blade? will I notice it?
Yeah mate a couple of pages back I listed pics from the calcs
Hey Officer Dan
1st pic is the before pic in 2011
2nd and 3rd pics is the now pic in 2019
No grass however the owner is putting a shed there so all is good in the hood
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OldDan1943
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Hey Officer Dan
1st pic is the before pic in 2011
2nd and 3rd pics is the now pic in 2019
No grass however the owner is putting a shed there so all is good in the hood
Then, the owner is happy. That's important.
If that's the case then I may not need an additional blade as i am currently running the 3 blade version of that 4 blade in the pic. The 4 blade is what austral said I could fit. What is the benefit of that extra blade? will I notice it?
Less blades = more efficient. More blades = easier to balance.
there are other items too.
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If that's the case then I may not need an additional blade as i am currently running the 3 blade version of that 4 blade in the pic. The 4 blade is what austral said I could fit. What is the benefit of that extra blade? will I notice it?
Mat, to be honest, I really doubt you'll need anything more than what you've got, and that $2600 better spent on other stuff. My Clipper 34 went extremely well with a 3 blade prop, with plenty of power, no cavitation, and the right sweet spot. Your boat weighs about the same as well.
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Nomad Willy
Guru
Peter do ya think Matt has the clearance?
If so you may be the perfect one to respond. Only real difference is probably the weight. An inch less pitch should even things out. For Matt’s research what dia and pitch and gear was in your boat? Looks real good to me but the gear ratio and clearance may take it out of a near perfect match.
Other owners of very similar boats could narrow it down.
Matt whats your prop clearence?
If so you may be the perfect one to respond. Only real difference is probably the weight. An inch less pitch should even things out. For Matt’s research what dia and pitch and gear was in your boat? Looks real good to me but the gear ratio and clearance may take it out of a near perfect match.
Other owners of very similar boats could narrow it down.
Matt whats your prop clearence?
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Eric, if you scroll back to his photo of his present set-up on the last page to Hendo's post #4718, you'll see his clearance is virtually exactly the same as mine was. Frankly I doubt that all this propellor stuff is really the fine tolerance rocket science some try to make it out to be, causing unnecessary anxiety. I suspect Matt Hendo's set-up will propel his vessel just fine.
BruceK
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I installed a 3 blade instead of 4, not as well balanced but does the job. In the toilet at home,so it`s a tough gig .
Save your $, Matt, see if there`s a problem after splashdown. My IG has 3 blade props and it`s fine. A boat I inspected with 4 cyl Cummins Bs changed to 4 blades,they replaced engine mounts, so? vibration. You`ve a Perkins 6, wait and see, lots else to spend $ on.
.Save your $, Matt, see if there`s a problem after splashdown. My IG has 3 blade props and it`s fine. A boat I inspected with 4 cyl Cummins Bs changed to 4 blades,they replaced engine mounts, so? vibration. You`ve a Perkins 6, wait and see, lots else to spend $ on.
Eric, if you scroll back to his photo of his present set-up on the last page to Hendo's post #4718, you'll see his clearance is virtually exactly the same as mine was. Frankly I doubt that all this propellor stuff is really the fine tolerance rocket science some try to make it out to be, causing unnecessary anxiety. I suspect Matt Hendo's set-up will propel his vessel just fine.
Thanks Pete. It’s really reassuring to know you had a similar set up, size and weight and you had no issues. Such a relief. You have no idea how much I’ve layed in bed tossing and turning worrying about this. Thanks mate
I installed a 3 blade instead of 4, not as well balanced but does the job. In the toilet at home,so it`s a tough gig
Save your $, Matt, see if there`s a problem after splashdown. My IG has 3 blade props and it`s fine. A boat I inspected with 4 cyl Cummins Bs changed to 4 blades,they replaced engine mounts, so? vibration. You`ve a Perkins 6, wait and see, lots else to spend $ on.
Ok cool. I’ll park it and worry about something else haha.
Nomad Willy
Guru
Glad he’s got a Perkins.
But Peter are the gear ratio’s the same?
That could make a huge difference.
But Peter are the gear ratio’s the same?
That could make a huge difference.
Well today was spent scratching up the whole boat in 320grit read for priming on Saturday and then I got the cut and polish out to clean up the glass door and fixed door panel. There has been a collection of crap that has been on them throughout the past 3 years. I haven’t bothered to clean them before but it’s time now so the buffing machine came out with some heavy duty cutting compound and now the glass doors are mint..!!! Just have to do the 3 windscreens and the 4 side windows now
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OldDan1943
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Good to know you are doing something. Thought we lost you again. Soon maybe, splash and then.... a long maiden voyage!!
Lou_tribal
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Right, good to know you are doing something, was thinking you just got a break to rest and procrastinate, I was worrying!
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Hey boys. Nah I’m still here. Had a little holiday looking at the Orca’s and swimming and fishing. I’m back now so hooking in again. Really loving the new place I’m at. Wish I’d made the move sooner.
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Lou_tribal
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My place is a bit like yours but without the sea and with snow instead of sand, but pretty much the same lol
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