Prop placing/angle etc.

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Greybird
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Joined: Wed Mar 18, 2015 3:17 pm

Prop placing/angle etc.

Post by Greybird »

I am in the process of building my 'Barrelback' in landlocked Oxfordshire in the UK. It is giong well but ... I know this has been answered a few hundred times but I cannot find a reponse to a question that I have been asked by a supplier in the UK.
Firstly I should predicate this by saying that if I buy boat bits from the USA they are very favorably priced but by the time they get back to the UK and the TAX we have to pay makes them prohibitively expensive so I am trying to get all the hardware here. That said I have had to get some bits from Michigan Motors who are very helpful indeed, thanks to them.
I have bought a remanufactured Mercruiser 4.3 litre V6 to which I have added a 1:1 Velvet drive. I am at the troublesome part of working out the what/why/when and where of positioning the prop/strut/rudder. I contacted a supplier here who said that a 12/12 propellor was not big enough for a 220/240HP engine and that it would 'cavitate'. I think that means that above a certain amount of revs it no longer 'bites' the water. They say I should have a 14" prop and a 1.25" shaft. Of course that changes the angle of the engine (which looks a bit tight already).
I took a lead from Greg Roy in New Zealand who I went to see when I was last there and have set the engine up on a rig so I can get it set up completely and run it before it goes in the boat. I also means that I can get the engine positioned for all the 'throught the hull' hardware, but I need to better understand this prop problem.
Any thoughts would be gratefully received!!!!
I made a blog as I did not think my friends (who asked me to do it) would log on to Glen-L. It is at http://greyfalcon.info
Here is a picture of where I am at!
IMG_5922.jpg

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Roberta
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Re: Prop placing/angle etc.

Post by Roberta »

I don't think a 14" prop or a 1-1/8" shaft are necessary. I'm running a 13x13 four blade OJ prop on a 1" shaft with a 330 hp Crusader V8. Works just fine. I would suggest mounting the engine and strut per the plan locations and use the recommended angle strut and place the rudder per plan.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

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Bill Edmundson
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Re: Prop placing/angle etc.

Post by Bill Edmundson »

Greybird

I don't have a set of BB plans. The shaft angle is usually 12* to the engine stringer, which usually makes it 12* to the keel. There should be 1 shaft dia. between the strut and forward edge of the prop. Leave enough space between the end of the shaft and the rudder for prop. removal.

With the 220/240 HP you will probably run 70 to 80 KPH at WOT. You should have 1 1/2" to 2" clearance between the prop and the bottom of the boat. That means that the a 13" dia. prop. is probably as large as you can go. The 13x13 sounds about right.

Bill4
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Greybird
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Joined: Wed Mar 18, 2015 3:17 pm

Re: Prop placing/angle etc.

Post by Greybird »

Thank you both for the input. I think some people are trying to complicate my life unnecessarily!!!

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kens
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Re: Prop placing/angle etc.

Post by kens »

With a 1:1 transmission, the 1" shaft is correct.
the accepted tip clearance for the prop is minimum 10% of diameter, and most of us run 15%
If you can properly fit a 13"diameter prop, you will be fine; at your sea trials you would only need to adjust for pitch if at all.
Build the project to fit a 1" shaft and 13" diameter; then at sea trials all other attributes of a prop can be exchanged out (pitch, # of blades, rake, cupping)
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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billy c
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Re: Prop placing/angle etc.

Post by billy c »

Run a 13x13 prop with a 1" shaft. You can get that to work best with the strut drop engine placement and shaft angle as drawn on the GlenL plans
(insert Witty phrase here)
Billy's Belle Isle website

falconer100
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Joined: Wed Nov 16, 2011 5:33 pm
Location: solihull UK

Re: Prop placing/angle etc.

Post by falconer100 »

Greybird

I am also building a Barrelback which is almost finished in Solihull UK. I placed the rudder and strut exactly as per the plans, the engine at 15 degrees with the strut at 18 degrees. The instructions recommend a 12" prop but I was also told that this was too small however one prop calculator website came up with a 12x19 prop giving a top speed of 78mph!!! I cannot fit a 14" prop as there is insufficient clearance from the hull, I am going to go with a 13x13 four blade and see how it performs.
A 1" shaft is more than sufficient, you don't need one any larger than that.
Have you tried speaking to Tides Marine in Poole, they are very helpful, they supplied me with the rudder, strut and seals, they should still have a copy of the plan showing the underwater gear placement and spec for the Barrelback.
Good luck with your build, it seems to be coming along nicely.
Martin.

falconer100
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Location: solihull UK

Re: Prop placing/angle etc.

Post by falconer100 »

Greybird

Having looked at your blog, its a shame I didn't see it earlier as I have a spare bellhousing you could have had gratis. :roll:

Greybird
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Joined: Wed Mar 18, 2015 3:17 pm

Re: Prop placing/angle etc.

Post by Greybird »

Hi Falconer100
Thankyou for the input, and everyone else as well.
Could we do an 'I'll show you mine if you show me yours?' I have only seen one other boat, finished, that's Greg's boat 'Bootlegger', but it would be great to see your build. How far have you got?
I am only down in Oxfordshire so Solihull is very nearby.
Let me know, you could email me through david@greyfalcon.info.
Thanks
David

falconer100
Posts: 75
Joined: Wed Nov 16, 2011 5:33 pm
Location: solihull UK

Re: Prop placing/angle etc.

Post by falconer100 »

Hi David,

It would be a pleasure to meet a fellow builder, I am currently installing the mahogany on the deck as the weather permits, although all the mechanicals are finished apart from selecting and fitting a prop.
If you would like to meet on a weekend that would be great, just let me know when it would be convenient
I tried emailing you but part of your address is missing. You can email me on martinbolton64@gmail.com
I look forward to hearing from you.

Regards,
Martin.

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Bill Edmundson
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Re: Prop placing/angle etc.

Post by Bill Edmundson »

Martin

If you give me HP (metric or standard), gear ratio, and best guess at your boats running weight. I'll try to give you an idea on props. Are you sure he wasn't talking KPH instead of MPH? MPH would imply nearly 500 HP in the US. KPH would be 48 mph at 230 HP in the US.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Greybird
Posts: 6
Joined: Wed Mar 18, 2015 3:17 pm

Re: Prop placing/angle etc.

Post by Greybird »

Hi Bill
Thank you for the response. The general concensus is that a four bladed 13 x 13 prop on a 1" shaft is what I need. The problem is I bought a recon engine and I am not sure of it's power, but as the speed limit on the Thames river is 4 knots and I live a hundred miles from the sea, I shall go to a local lake where I doubt I shall be going too fast!
Thanks again
Greybird

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kens
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Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Prop placing/angle etc.

Post by kens »

Agreed that you need 1" shaft and 13" diameter, however,
it is too early in the build to say you need 13" pitch or 4blade vs 3blades.

There is a great many V8's in runabouts running 3 blades.
Just because 1 guy runs 13 pitch 4blade doesn't necessarily mean your boat will require that,
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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Roberta
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Re: Prop placing/angle etc.

Post by Roberta »

A 13 pitch four blade might be too much for a V6 at 220 HP. I'm running a 13X13 four blade on my Torpedo with a 330hp V8. Even the 12X12 might be a good starting point for your V6.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

falconer100
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Joined: Wed Nov 16, 2011 5:33 pm
Location: solihull UK

Re: Prop placing/angle etc.

Post by falconer100 »

Hi Bill,

Nice to hear from you again.
It was definitely mph, not that I would ever want to go that fast with a Barrelback hull (vertical stem and deep forefoot?). I'm running 200HP with a velvet drive 1.1 direct drive with a 1" shaft. The boat is a standard 19' unstretched. I would, at a very rough guess say the weight is about the 1200kg mark. Before I fitted the engine, I could lift the back of the boat off the cradle single handed.
Roberta, I spoke to a prop company at the Southampton boat show about a 12x12 and all I got was "you may as well put an egg whisk on it" ... rather rude I thought.

Martin.

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