We have an issue where there is only 1/8" clearance between the port prop and the strut, but almost 2" between the stbd prop and strut. The port shafts are connected with a 10 1/4" muff coupling, while the stbd shafts are connected with a 12 1/4" muff coupling. This would seem to explain the difference in clearances between stbd and port. However, Sams says that the correct size muff coupling is 10 1/4". My question is, what should the clearance be between the strut and prop? Surely it should be more than 1/8", correct? And what might another source of this lack of clearance be? It is a 1978 53' MY. In other words, if the 10 1/4" muff coupling is correct, why is the prop almost touching the strut?
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Thread: Prop / Strut Clearance
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09-19-2018 04:02 PM #1Senior Member
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Prop / Strut Clearance
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Re: Prop / Strut Clearance
There is a formula for that spacing, i think its 50% of the shaft diameter but i couod be wrong. so for a 2" shaft it would be 1"
Somone must have replaced the shaft or coupler at some point...Pascal
Miami, FL
1970 53 MY #325 Cummins 6CTAs
2014 26' gaff rigged sloop
2007 Sandbarhopper 13
12' Westphal Cat boat
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09-19-2018 04:51 PM #3Senior Member
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Re: Prop / Strut Clearance
Yeah, we are going to have to measure things closer to get to the bottom of this. Any ideas on how to eek out another 1/2" of clearance? I wonder if the transmission couplings are the culprit. In other words, they were too short and they addressed this on the stbd side with a longer muff coupling, but not on the port side (because they couldn't find a second longer muff coupling).
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Re: Prop / Strut Clearance
Pascal, I always thought it was shaft diameter, not half of.
Maybe I'm thinking about distance between strut and prop???
But, Michigan Wheel ideally wants 20% of prop diameter to be the difference, 15% is the minimum.
"The clearance between the propeller blade tips and the hull bottom should be at least 15% of the propeller diameter and ideally, 20% or more. So for example, a 20” diameter propeller would have 3” minimum clearance and better still 4” or more. A common guideline for recommended propeller to strut or keel clearance is 20% of propeller diameter measured between the propeller blade edge and strut leg or keel. This is often measured at a point on the propeller blade edge about 70% of the distance from the shaft centerline to the blade tip."
https://www.miwheel.com/resources/faq/inboard/CRICKET
1966 HAT50C101
Purchased 1985 12v71Ns
Repowered 1989 with 8v92TI
Repowered 2001 with 3406E
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Re: Prop / Strut Clearance
I think you re right, it is shaft diameter not half
Pascal
Miami, FL
1970 53 MY #325 Cummins 6CTAs
2014 26' gaff rigged sloop
2007 Sandbarhopper 13
12' Westphal Cat boat
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09-19-2018 05:38 PM #6
Re: Prop / Strut Clearance
Hatteras should have all the measurements for the shafts, couplers and what the original props were. I doubt it left the factory that way. It's possible someone did some work and changed out a shaft or coupler.
I believe 1/2 the shaft diameter is the maximum space between the prop and bearing. I've also seen spacers added at the transmission coupler that absorbed vibration or something like that. Not really the way I'd do it though.Scott
41C117 "Hattatude"
Port Canaveral Florida.
Marine Electronics and Electrical Products Distributor.
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09-19-2018 06:54 PM #7Senior Member
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Re: Prop / Strut Clearance
Is the hole through the muff coupling all the way through? In other words, are the two shafts butted up against each other? This is what the couplings I have seen are like. In which case, whether the coupling is 10 1/4" or 12" wouldn't make a difference to the overall shaft length, which points to the shaft being too short.
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09-19-2018 08:37 PM #8Senior Member
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Re: Prop / Strut Clearance
Something like this? ...
https://propshopinc.com/Drivesaver-5...756A-p678.html
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09-19-2018 08:40 PM #9
Re: Prop / Strut Clearance
I dont know if theres one large enough though. I've not seen one on a hatt.
Scott
41C117 "Hattatude"
Port Canaveral Florida.
Marine Electronics and Electrical Products Distributor.
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09-19-2018 10:01 PM #10
Re: Prop / Strut Clearance
max distance is shaft diameter, less is better so you dont get as much whip. i'm sure 1/8 is too close, being that small of a gap might slow the water flow down thru the bearing