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Old 26-11-2012, 18:07   #1
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Raw Water Thru hull

After 5 month's on the hard I,am ready to relanch.As I,was getting ready to purchase new thru hull fittings when I,beame aware my raw water intake is 1/2 inch and all lines leading from the valve to the engine are 1 inch.During the trip home a 1000 miles plus trip I,encountered no problem's except when I,grounded once and pushed hard to get off the temp rose.Do I need to enlarge my thru hull to 1 inch?The engine is a Yanmar 4JH3E 56 hp.
Thank's to all
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Old 26-11-2012, 18:21   #2
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Re: Raw Water Thru hull

Perhaps you can change it out next time you are on the hard, if you are not having overheating issues now. Of course, the temps outside right now are not very hot...

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Old 26-11-2012, 18:26   #3
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Re: Raw Water Thru hull

Your manual should give the minimum size needed for the intake.
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Old 26-11-2012, 18:39   #4
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Re: Raw Water Thru hull

I have a Yanmar 3GM30F. I use a 1" seawater intake for my engine to ensure plenty of water when things get tight (kelp or plastic bags plugging the intake, etc.). I have a 1/2" thruhull forward for the head and saltwater washdown, and a 1/2" aft for the saltwater pump to the galley and the reefer cooling. Don't be stingy about cooling stuff.
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Old 26-11-2012, 18:43   #5
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Re: Raw Water Thru hull

If you ran at max RPM it would be a bit too small. That is it has too high a pressure drop to flow the required GPM at full rated HP.
But I'm betting your running below 25-30 hp on a 38' hull which is probably OK for the 1/2" (barely)

Me I might put a larger thru hull on the list for the next haul out. But I'd not pull the boat just to replace the thru hull at this time. It did fine for a 1000 mile run....

BTW rubber hose has a much higher pressure drop per gpm then smooth solid pipe, so its not quite as bad as it looks.
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Old 26-11-2012, 19:35   #6
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Re: Raw Water Thru hull

As sailorchic says size does matter. you also have to consider some marine growth on the inside of the thru hull. This will further reduce the volume of water coming in. Additionally you do not want your water pump to have to pull too hard to get the water flowing this could cause cavitation in the pump and reduce impeller life. So go bigger if you can
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Old 26-11-2012, 19:58   #7
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Re: Raw Water Thru hull

A half-inch opening is undersized for the raw water cooling inlet of an engine of that horsepower. Don't chance it, change it out to what the manufacturer recommends.
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Old 26-11-2012, 20:23   #8
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Re: Raw Water Thru hull

In my experience, you will need 1" raw water inlet for 56 hp. Ask your Yanmar dealer.
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Old 26-11-2012, 20:42   #9
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Re: Raw Water Thru hull

Since you're hauled out now, spend another hour or two and change it out.
Take the opportunity to install a real seacock as well. I'm guessing you're using a ball valve screwed onto the thru-hull now as I don't know of anyone who makes a real seacock in 1/2". Now that I think about it, it's pretty hard to attach 1" I.D. hose to 1/2" pipe. Are you sure it's 1/2"?
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Old 27-11-2012, 05:17   #10
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Re: Raw Water Thru hull

Thank's for all the response.100% right it is a 1/2 thru hull going to a 1/2 ball valve with a connector to 1 " hose to engine.I,am still on the hard and will up it 1" the whole route.No room for a seacock.Will have to go thru a ball valve arrangement again.Not enough height and ball lever must open and close side to side .PO when installing new engine got lazy or cheep,Had to upgrade exhaut to 3" from 2" also.The Joy's of Boating.
Thank's again Folk's Dave
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Old 27-11-2012, 07:47   #11
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Re: Raw Water Thru hull

Since you don't have room for a real seacock, think about using a Groco Flanged adapter with your thruhull and ballvalve. It solves the problem of mismatched threads that occurs when you screw a tapered thread ball valve onto a straight thread thruhull. It also gives you a flange that can be fastened to the hull.

Groco Flanged Adapter IBVF
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Old 27-11-2012, 08:48   #12
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Re: Raw Water Thru hull

Quote:
Originally Posted by HopCar View Post
Since you don't have room for a real seacock, think about using a Groco Flanged adapter with your thruhull and ballvalve. It solves the problem of mismatched threads that occurs when you screw a tapered thread ball valve onto a straight thread thruhull. It also gives you a flange that can be fastened to the hull.

Groco Flanged Adapter IBVF
+1 on the Groco Flanged Adapter. My plan is to use them when I replace all the thruhulls with ball-valves on my CR-38.
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Old 27-11-2012, 09:53   #13
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Re: Raw Water Thru hull

Look inside the ball-valve. Most of them step down in size at the ball. Only a few are "full flow".

Better, try to find some of the old Groco valves that could be disassembled. That's all I use. Thirty-five years old and good as new.

Here are some pics showing the arduous process of overhauling the seacocks:
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Old 27-11-2012, 16:53   #14
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Re: Raw Water Thru hull

Quote:
Originally Posted by HopCar View Post
Since you don't have room for a real seacock, think about using a Groco Flanged adapter with your thruhull and ballvalve. It solves the problem of mismatched threads that occurs when you screw a tapered thread ball valve onto a straight thread thruhull. It also gives you a flange that can be fastened to the hull.

Groco Flanged Adapter IBVF
Thank's I,have a unique sitituation.I,have to make a 90 degree turn immediately after passing thru the hull.As it is now I,have to cut the thru hull and fit a 90 degree street elbow which I,am able to secure to the top of the thru hull nut some backing there the 90 also meshes with the thru hull same thread's.Other end receives a full flow ball valve and 1" hose fitting.I,have just used 2 of the Groco flanged seacocks secured to backing block's the way compass marine suggest.Worked out ok.I,am bringing all thru hulls up to proper standard,unbeleivable to me that a supposed quality boat would leave the Factory with ball valves screwed to thru hull's.I,had one break year's ago simpley trying to unfreeze a frozen ball valve.Once bitten twice shy.
Thank's for all the input Dave
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Old 27-11-2012, 16:56   #15
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Re: Raw Water Thru hull

Quote:
Originally Posted by Roy M View Post
Look inside the ball-valve. Most of them step down in size at the ball. Only a few are "full flow".

Better, try to find some of the old Groco valves that could be disassembled. That's all I use. Thirty-five years old and good as new.

Here are some pics showing the arduous process of overhauling the seacocks:
Had them on my C&C for 20 plus year's,Best thing since sliced bread.
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