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Old 02-09-2016, 07:40 PM   #21
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My knee jerk reaction would be that none of that will work. Maybe with a 1 to 1 gear that 1&1/2 inch shaft would be big enough. Splitting the exhaust is a really bad idea. None of your current setup will be useable. The prop and shaft are way to small to utilize 375 hp. You really need to get a knowledgeable marine engineer or at least consult with a yard that knows what theyre doing. Can you make it work ??? yeah. Would it be right??? NO. Derating is still a viable option.
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Old 02-09-2016, 07:46 PM   #22
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I dont know what gear you have now but its my opinion that your current setup is marginal (shaft size and exhaust) for the engine you have. Gas big blocks use that size stuff. Going up in power will be VERY expensive just in installation costs. Everything will need upgrading. Dont take my word for it, get a trusted professional opinion. They will tell you the same thing.
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Old 02-09-2016, 08:36 PM   #23
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Originally Posted by kulas44 View Post
I dont know what gear you have now but its my opinion that your current setup is marginal (shaft size and exhaust) for the engine you have. Gas big blocks use that size stuff. Going up in power will be VERY expensive just in installation costs. Everything will need upgrading. Dont take my word for it, get a trusted professional opinion. They will tell you the same thing.


Actually, since your last post I downloaded the "Caterpillar Marine Engine Applications & Installation Guide" Copyright 2000, and though you are spot-on about my gear being way too light for 375Hp, a 1 1/2" stainless shaft is completely appropriate for my 3208NA.
It appears that I should be looking at something like 2 1/4" shaft size.
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Old 02-09-2016, 08:43 PM   #24
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Don't think you have enough prop diameter to utilize the HP to get the boat over the hump onto plane. Repower my downeaster from 210 to 300 HP. Had to change motor mounts (heavier engine ), shaft, shaft tube, exhaust, and the prop. Mechanic put it simply, need a bigger prop to convert HP to push.

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Old 02-09-2016, 08:44 PM   #25
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You will probably need a 2" prop shaft for the 375 hp Cat. My 34T with the Yanmar 370 had a 2" shaft.

Your current NA 220 hp Cat probably has an 1-1/2" shaft. So it will take a new shaft, prop and strut to make this change work. That is a minimum of $5,000 for all.

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Old 02-09-2016, 08:46 PM   #26
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Welcome and good luck with your re-power.
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Old 02-09-2016, 09:17 PM   #27
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A 1.5" shaft can handle a 375 depending on gear ratio. A little on the light side, but ok at 1.5:1. Cabo sportfish with 435 3208's came factory with 1.5:1 gears and 1.75" shaft.
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Old 02-09-2016, 09:24 PM   #28
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Thanks to all who have responded thus far.
I knew going in that my prop was no good, and I suspected that the shaft, and strut were too small. All your responses, and what I've managed to research today while this thread developed has confirmed all that.
Having said that, I'm not yet convinced that this is out of the question.
If it happens, it's going to be in a DIY storage yard with minimal out sourcing. I have a "Caterpillar go-to guy" who I will discuss the exhaust issue.
David. I think you're probably pretty close when you quote $5000. for shaft & assoc. components. That's do-able.
Swapping the engine will be no big deal, and I'm prepared to be in the yard a long time,
and I'm preparing to own the boat a long time.
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Old 02-09-2016, 09:29 PM   #29
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A 1.5" shaft can handle a 375 depending on gear ratio. A little on the light side, but ok at 1.5:1. Cabo sportfish with 435 3208's came factory with 1.5:1 gears and 1.75" shaft.
That's good to know; Thanks.
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Old 02-09-2016, 11:25 PM   #30
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Is this boat light enough to preform on plane? Getting there and performing there are two different things.

Weight becomes a much more important part of the package. The difference between planing freely and laboring to just make the grade (bow wave) is night and day.
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Old 02-10-2016, 01:26 AM   #31
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Does the boat have enough hull clerence to swing a larger diameter wheel?
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Old 02-10-2016, 05:26 AM   #32
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Haywayn

Suggest you take a day and drive over to Oxnard and talk with Tony Athens. The initial phone or email call will be a data, hopes and dreams exchange with him. As already mentioned, props move boats. IMHO that is your starting point, not the engine.
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Old 02-10-2016, 06:33 AM   #33
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The issue with all of this that would scare the crap out me is the point that RTF touched on: the engine has sat unused for over 15 years. So, its only done 100 hours? But its condition, and what it may well cost you once you own it, really depends on how it has been stored. In this case low hours is problematic, not an advantage.

Get your Cat go-to guy on the case to take a good look at it, fire it up when ready to do so, and test it as thoroughly as you possibly can before handing over anything more than a deposit.

Nothing to add to other posts about things needing to be changed, possible benefits etc. Other than it will end up costing you twice as much as you expect even if the there are no R&M issues with the 375HP engine.
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Old 02-10-2016, 07:52 AM   #34
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Prop clearance is just one of numerous issues. Bigger diameter to utilize added hp will need new taller strut and larger shaft, bigger prop/taller strut means different shaft angle neccessitating new engine installed angle requiring new engine beds and mounts. More hp needs more raw water flow requiring bigger thru hull and strainer. Basically a complete repower. All of this and you still have an antique engine. Any modern inline 6 that would fit would be better.
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Old 02-10-2016, 09:15 AM   #35
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dumping all that money into an old boat is unlikely to ever get a return. Why are you so sure the old engine is toast?
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Old 02-10-2016, 10:35 AM   #36
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From my files:

A client had a 37' Angel sport fisherman style boat powered by a pair of Iveco strait 6s. He found a "can't pass this up" deal on a pair of Cat 6s that would give him an extra 5 knots at cruise. Next he found a boat yard mechanic who could do the swap for a satisfactory fixed price.
Old story, but once into the swap the mechanic found that it wasn't as easy as he had figured, so he asked for more money, then when my guy wouldn't add to the pot, stopped work. My guy pulled the job, went to another mechanic, and came to me for the lawsuit.
The swap was done, including: new stringers so the wider stance of the Cats would fit and the whole works could be moved fwd, so the shaft angle would stay the same with the bigger shafts and taller props, new exhaust runs for the larger diam outlets, new floors above for the bigger, relocated access hatches, and so on.
What had been originally estimated at $40k went well over $100k, and recovery by way of the lawsuit was limited, as the original guy had next to nothing.
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Old 02-10-2016, 06:55 PM   #37
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Ask Tony Athens as suggested he has done hundreds of repowers and will know all you need to know including price and feasibility.
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Old 02-10-2016, 07:46 PM   #38
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Quote:
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From my files:

A client had a 37' Angel sport fisherman style boat powered by a pair of Iveco strait 6s. He found a "can't pass this up" deal on a pair of Cat 6s that would give him an extra 5 knots at cruise. Next he found a boat yard mechanic who could do the swap for a satisfactory fixed price.
Old story, but once into the swap the mechanic found that it wasn't as easy as he had figured, so he asked for more money, then when my guy wouldn't add to the pot, stopped work. My guy pulled the job, went to another mechanic, and came to me for the lawsuit.
The swap was done, including: new stringers so the wider stance of the Cats would fit and the whole works could be moved fwd, so the shaft angle would stay the same with the bigger shafts and taller props, new exhaust runs for the larger diam outlets, new floors above for the bigger, relocated access hatches, and so on.
What had been originally estimated at $40k went well over $100k, and recovery by way of the lawsuit was limited, as the original guy had next to nothing.
I can picture that. Both cost and sad scenario for all involved. My repower was with new JD 6068's that were about $60k including wiring harnesses etc, so I probably got close to 100k all in. I don't know exactly as it was part of a lot of other work. So maybe $40k with free engines is possible?

I was able to keep existing shafts, struts, props but did spend $9k on gearbox overhaul/rebuild. The OP will not be able to avoid any of these. I needed a new exhaust system, replaced water intake filters etc. Once you start you do find extras and you need to keep going, and should avoid short cuts. Do it right, just wear the cost.
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