Agree, a baseline is in order. Unknown history, mismatched components and questionable data,... the acronym GIGO comes to mind. The whole thing needs to be looked at from square one.
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Thread: WTH do I do with this?
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Re: WTH do I do with this?
--- The poster formerly known as Scrod ---
I want to live in Theory, everything works there.
1970 36C375
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08-15-2017 07:07 PM #12Senior Member
- Join Date
- Jan 2014
- Posts
- 164
Re: WTH do I do with this?
First off. 55C's came from the factory with 32" wheels. So the mystery deepens as to why your WOT RPMS are low.
What HP are your 1271's? How many hours on them? Do you know when was the last time the timing was set and the racks adjusted? Lots of things play into low RPM's other than the props.
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Re: WTH do I do with this?
Deeper still. My owner's manual shows 30" props. I believe majority of the 55s were, as you say, 32" with Allison 2:1 gears adverting 650HP. Mine is ZF 1:1.51 with original rating of 850HP. There's at least some justification for Ageless' 28" wheels. PO of mine left me with a set of 28s. Said it jumped up on plane but lacked the top end of the 30s by a knot. Loooots of variables. Anyone looking for a nice set of balanced 28 X 28s?
Semper Siesta
Robert Clarkson
ASLAN, 1983 55C #343
Charleston, SC
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08-15-2017 09:44 PM #14
Re: WTH do I do with this?
did not have an engine survey, based on the extensive maintenance records provided and the engines performance during survey (minus the 200 RPM's under load) I was confident in their condition.
the vessel had 15 hours on it in 3 years, the fuel filters have 20 hours max on them, bowls look cleanLast edited by ageless; 08-15-2017 at 09:56 PM.
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08-15-2017 09:50 PM #15
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08-15-2017 09:53 PM #16
Re: WTH do I do with this?
Last edited by ageless; 08-15-2017 at 09:58 PM.
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08-15-2017 10:00 PM #17
Re: WTH do I do with this?
I'm thinking a call into Hatteras may be in order to clarify the wheels
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Re: WTH do I do with this?
I hate to say this is interesting, because the last thing you want to have is an "interesting" problem. Interesting usually equates to expensive.
But I agree with those who feel you should zero out the engine variables, if that's the right term, before looking at the wheels. The problem is that there are so many other potential causes of this kind of odd behavior on the part of the boat.
It seems to me that you can make a pretty good argument for the idea that the power curves or output differs a lot from one engine to the other. Unfortunately, putting your engines on a dyno to check what they are really doing is impossible.
But you might be able to get close by seeing what the high idle is on each one, verifying that the racks are opening all the way, and that all cylinders are firing reliably. Also that you don't have excess frictional losses anywhere in either driveline (bad cutlass bearings, etc) and that the props scan to the reported measurements accurately. I assume both gears are the same ratio- a friend of mine chased unequal power and fuel use for years only to finally figure out that he had two different gear ratios P&S- he wasn't happy to say the least.
Good luck on this. I hope you're able to get to the bottom of it. No pun intended.
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08-16-2017 08:10 AM #19
Re: WTH do I do with this?
I intend to do just this Jim, will dive into the injectors and rack this weekend. If there was an issue within either of these would it present itself only under load?
Without tearing into the gears, I'm ASSuming the only way I can verify ratios is by the plates on the side and they both DO reflect 1.51:1. The vessel is on the hard and I didn't detect any play in the shafts before removing the wheels, had planned to put a dial indicator on them this weekend prior to this prop finding.
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08-16-2017 09:05 AM #20Senior Member
- Join Date
- Jan 2006
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- 821
Re: WTH do I do with this?
There's no standard wheel for any particular model boat. The only thing that you should worry about is the engines being able to reach it's rated rpm under load. Have the wheels made the same at the lower pitch and see what it turns. See if the yard will haul at a reduced rate if you need to fine tune the pitch. There's no way to know what going to happen until you make a change then go run the boat. A full tower will make a substantial change in prop size