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 Post subject: Specifications??
PostPosted: 14 Feb 2016 12:04 
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Able Bodied Seaman

Joined: 01 Dec 2013 04:38
Posts: 31
Hi everyone,

I'm in the process of ordering a Varifold propeller for my 1979 37c and went to the dealer with double the amount of money I told my wife I had..... (every sailor does that right?)

Anyways, he started asking all kinds of questions I had no answer for, so we went to this site and it was down... (First time ever for me) He wanted specific weight, waterline length ect.. When we started searching, we found there was quite a difference in waterline lengths/overall lengths and even beam. I was specific on 37 C /37-2 but found varying numbers. I do not believe the factory would have changed molds to the extent that they changed the waterline length from 31'7" to 28'-5" to 29'-5"? They vary too much to be typos, and I can understand a few inches here or there, but 2 feet?

Does anyone have the holy grail of specifications?

Thanks, Jeff


 
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 Post subject: Re: Specifications??
PostPosted: 15 Feb 2016 08:22 
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Midshipman

Joined: 01 Nov 2014 12:50
Posts: 68
Location: Toledo
I think the confusion may be that the waterline increases as the boat heels when under sail.
The 28'6" Datum Waterline would be pretty much the measurement at rest and probably not fully loaded with fuel, water, and crew. Other waterline measurements for the Tartan 34C are likely at certain heeling angles.

FWIW our 1976 Hull # 4 is powered by a Westerbeke 40
We are currently using a 2-blade Max-prop 17" feathering propeller with pitch set to 11.6 (20 degrees)
we are reaching 6.4 knots at 2200 rpm.
6.6 @ 2400 (80% throttle)
Have not done much WOT testing but I imagine we wont quite hit 7 knots. I will check into that some other time.

This might be useful information to your prop dealer... but what I am lacking is the transmission drive ratio... which is vital to know SHAFT RPM versus ENGINE RPM when making prop comparisons. It might be 2:1... I forgot, and with the boat covered up and on the hard it will be tough to check for you...


 
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 Post subject: Re: Specifications??
PostPosted: 15 Feb 2016 16:59 
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Able Bodied Seaman

Joined: 01 Dec 2013 04:38
Posts: 31
Thanks Kent,

I have repowered with a beautiful 3j4he Yanmar a few years back so I don't need those numbers. However, I did measure my prop which is a 16 inch 2 blade which leaves about 1 inch between the top of the prop and the hull. I am curious if it was any closer it might cavitate? Mine is a 79.


 
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 Post subject: Re: Specifications??
PostPosted: 15 Feb 2016 21:32 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 656
I have a 17" AutoStream on my Tartan 37 and Yanmar 3JH4E. I put a new shaft in when I was doing the engine replacement and I might have put it in a bit longer, but I had 1 and a half inches of clearance and have no trouble swinging it. I would not go less clearance. The folks at Martec suggested and David Gerr confirms in his book "Propeller Handbook" that you want to swing the biggest prop you can fit, but you do need clearance of a bit or you can get vibration or cavitation. I have had neither with mine. I have not measured the pitch, but I think Kent's numbers look right and would be a great starting point. I have adjusted the pitch on mine a bit (it is externally adjustable) depending on the type of cruising I am doing. When the boat is heavy for cruising, turn the pitch back a bit. When I am light turn it up. I also think that every boat and every engine has a touch different setting. That is why I suggest an externally adjustable feathering propeller.


 
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 Post subject: Re: Specifications??
PostPosted: 15 Feb 2016 21:40 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 656
I have a 17" AutoStream on my Tartan 37 and Yanmar 3JH4E. I put a new shaft in when I was doing the engine replacement and I might have put it in a bit longer, but I had 1 and a half inches of clearance and have no trouble swinging it. I would not go less clearance. The folks at Martec suggested and David Gerr confirms in his book "Propeller Handbook" that you want to swing the biggest prop you can fit, but you do need clearance of a bit or you can get vibration or cavitation. I have had neither with mine. I have not measured the pitch, but I think Kent's numbers look right and would be a great starting point. I have adjusted the pitch on mine a bit (it is externally adjustable) depending on the type of cruising I am doing. When the boat is heavy for cruising, turn the pitch back a bit. When I am light turn it up. I also think that every boat and every engine has a touch different setting. That is why I suggest an externally adjustable feathering propeller.


 
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 Post subject: Re: Specifications??
PostPosted: 16 Feb 2016 19:05 
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Midshipman

Joined: 01 Nov 2014 12:50
Posts: 68
Location: Toledo
Generally they say 10%-15% of the Diameter should be the prop tip clearance. I think the 17" on our boat is quite a bit closer than that though...
We have not had any cavitation issues, nor did I see any prop-wash damage to the paint there.
The real issue is likely excess vibration from the effect of the prop wash "bouncing" back off the hull onto the prop. I am guessing with a longer prop shaft, or shorter diameter prop It might be quieter. There is a "whooshing" sound the prop makes in gear. I don't have a lot of experience with feathering props(or other Tartan 37's), so I don't know if it is normal or not.
As far as my numbers go, they might be helpful to a technician to know what size prop is swinging at what speeds to attain hull speed. Then they can determine what your engine will be turning at and what the difference in horsepower is to determine a starting point for propeller trials.
I think you can also do a search in the forum's history and see a lot of other people propeller selections for different engines.


 
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