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Barracuda strut to prop distance

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Got Tiques Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 1:42pm
Bruce, Now I remember another reason I shortened my shaft. There was not enough shaft to rudder clearance with the original shaft to mount a 1210 prop. PO prop could be assembled, but the 1210 has way more metal nearer the center.
Yup, one more factor in the equation. Happy New Year!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 1:51pm
Originally posted by 8122pbrainard 8122pbrainard wrote:

Bruce,
What exactly are you looking for? From the start of the thread, it sounds like just a shaft length? 

Originally posted by Riley Riley wrote:

Just the shaft length.  Looking for the base line as we cut ours down to "optimum" length.
That's what I thought. 
Originally posted by TRBenj TRBenj wrote:

 
Those are the types of things (amongst others) that you should be checking before going down any errant paths with shaft lengthening. 
I'm sure glad you aren't going down some "errant paths". Seems Timmy forgets all the times he has recommended shortening shafts so the prop runs close to the strut. 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 6:23pm
Pete, I think your reading comprehension is really falling off these days.

Bruce is talking about adding 2+” back into his shaft length... aiming to restore the original 2.5”+ overhang (against the strong recommendation of at least one person here).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 6:46pm
Originally posted by TRBenj TRBenj wrote:

Pete, I think your reading comprehension is really falling off these days.

Bruce is talking about adding 2+” back into his shaft length... aiming to restore the original 2.5”+ overhang (against the strong recommendation of at least one person here).

Tim,
I know he wants to go back to the original length. How is that an "errant path". The overhung load issue? 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 6:57pm
Because every tidbit of reliable information on the subject, combined with a pretty reasonable amount of personal experience (especially in overpowered boats) says that minimizing that dimension is optimal from a reliability and performance perspective.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 7:27pm
Originally posted by TRBenj TRBenj wrote:

Because every tidbit of reliable information on the subject, combined with a pretty reasonable amount of personal experience (especially in overpowered boats) says that minimizing that dimension is optimal from a reliability and performance perspective.

In your experience what exactly happens without minimization? "reliability and performance perspective" is pretty vague. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 8:24pm
Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by TRBenj TRBenj wrote:

Because every tidbit of reliable information on the subject, combined with a pretty reasonable amount of personal experience (especially in overpowered boats) says that minimizing that dimension is optimal from a reliability and performance perspective.

In your experience what exactly happens without minimization? "reliability and performance perspective" is pretty vague. 

 

Pete, It must have something to do with this "overhung load" you speak of when your shaft is too long. From a thread sometime in the past 



Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by TRBenj TRBenj wrote:

Originally posted by Dieseldawg Dieseldawg wrote:

I have to ask, what will be the benefit of shortening the prop shaft?
 
The less shaft length you have hanging out past the end of the strut, the less stress will be put on the shaft.
 
And the cutlass bearing. 

Matt, 
As a mechanic, you should know this. In mechanical engineering terms, it's called "overhung load"!    A basic principle of physics and the use of a lever.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: January-02-2021 at 8:36pm
We don’t need my testimonial- but I think it’s relevant to hear Bruce’s theory on how reducing that shaft to prop dimension caused problems.

Based on my reading and experience I think it’s highly likely there is something else going on- maybe it was induced by shortening the shaft or maybe it’s another rigging or set up issue, possibly related to the installation of a significantly heavier, more powerful engine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 6:41am
The overhung load is a given but what are the performance problems?  Besides the cavitation Bruce,what other, handling issues are there? Tim? 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Riley Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 8:53am
I simply want the original spec to use for a base line.  How much length gets added to the shaft will depend on moving the shaft into different places and making a decision.  

There are 2 things to consider, prop to strut clearance which affects shaft performance, and prop to hull clearance which affects boat performance.  I don't see how anyone can disagree that shaft performance is secondary to boat performance. If perfect shaft performance is causing poor boat performance, what good is the perfect shaft performance?

In the case of the Cuda, Correct Craft put long shafts on them for a reason. While some people might cringe at the sight of their excessive prop to strut distance, they perform well and have been running like this since the 1960's.  In our case, we went with a short shaft in order to have perfect shaft performance as we were installing an engine that had 300 hp, much more than what was in the boat originally, and we knew it would require more prop, which it did.  We went from 12x13 to 12x16.

I've explained the handling characteristics on page one.  Based on my experience with 2 Cudas, I believe lengthening the shaft will be an improvement and make the boat handle better as it did with the longer shaft.  I'd rather not go to 2.5", but certainly .5" is inferior as far as boat performance goes to the original spec of 2.5".

As far as weight of the engine, I cannot find an Interceptor spec that has the weight of the FE marine engine.  I did find automotive specs that have the 318 at 550# and the 427 at 650#.  Chrysler Marine states that the 318 was 750# with all their beefy marine parts on it.  Given all of the light aluminum parts that the Interceptor has, I'd bet the 2 marine engines weigh about the same and the Interceptor maybe slightly lighter.  

This isn't rocket science and I often think some of us are overly critical of some of the things Correct Craft did in building their boats.  The long shaft on the Cuda may have been an unorthodox fix to enhance boat performance, but it worked.  

I simply want the original spec so that we have a base line. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 10:05am
Thanks Bruce,
Keep us informed how it works out. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 10:18am
Bruce 

It sounds and looks like you have the original spec between the picture of Charlie and the measurement numbers from Charlie by way of Pete

What I wonder about is your comment on the rudder port that is not mounted flush but sticks down from the bottom of the hull.

Was that bigger rudder and new port on there before the problem started or was it put on to try and solve the handling issue?

You mentioned Reid thinking that might be the problem, you can add me to that list.

Is it hanging down say 1/4 inch or so with squared off edges or is it tapered so it's at least somewhat hydrodynamically efficient

If you recess it like it was originally built, you'll be back to "baseline" there too



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Riley Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 10:30am
The rudder port is an issue and will be recessed.  It did not cause any problems prior to the engine swap, however.  The problems I noted on page one I know to be from the shortened shaft as I've experienced them with another Cuda.    I tried to install an original rudder port, but the hull has been altered to except the newer style port.  This was done by a PO.  

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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 10:42am
Sounds like longer shaft time.

Plenty of CC's had a lot of strut to prop clearance over the years.

Gen 2 SN's and the Martiniques on that same hull come to mind with over 2 inches of distance.

You have the info you wanted, you know the boat, I'd go with what you think needs to be done right now Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 11:20am
Not to throw a curve ball at you Bruce, but if you look closely at your strut and Charlie's strut they're not the same so any measurements from his may not really be what you're looking for if you're trying to get the prop location in it's original spot.

If you took an inch or so off of Charlie's, it would look like yours




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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 11:50am
Bruce,
Yes, the struts are different. Looks like you have a 6A and Charlie's is a 6A6. The 6A6 is 1 inch longer at the aft end so, that really puts the prop farther aft. I'd say the aft move was due to CC going to a 13" prop. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 1:19pm
Originally posted by 8122pbrainard 8122pbrainard wrote:

Bruce,
Yes, the struts are different. Looks like you have a 6A and Charlie's is a 6A6. The 6A6 is 1 inch longer at the aft end so, that really puts the prop farther aft. I'd say the aft move was due to CC going to a 13" prop. 

Further aft of what?

They're both 17 ft Barracudas, assuming the transmissions are mounted in the same spot and the struts are in the same spot and you put a 41 inch shaft for example in both, the prop is in the same spot on both boats.

On the boat with a 6A6 it sits closer to the strut by an inch though since the difference in the struts is all at the back. Trim an inch off the back of a 6A6 and it's the same as a 6A

I guess you'll have to explain how that gives any more room for a bigger prop Pete Wink


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 2:01pm
Originally posted by KENO KENO wrote:

I guess you'll have to explain how that gives any more room for a bigger prop Pete Wink 

Sorry but I'm not a math teacher


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Riley Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 2:59pm
All things being equal, Charlies strut would allow for less prop to shaft distance as the strut reaches farther aft.

Anyway, I appreciate the info and welcome any more measurements I can dig out.  Our original shaft was bent pretty badly, but maybe I can dig it out if it didn't go to the scrap pile.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: January-03-2021 at 3:15pm
Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by KENO KENO wrote:

I guess you'll have to explain how that gives any more room for a bigger prop Pete Wink 

Sorry but I'm not a math teacher

 
Pretty poor attempt at avoiding the question Pete Wink
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