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Old 03-11-2012, 11:42 PM
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Default Thru-hull fittings, intakes, and strainers - Inboards

Hello all!

Firstly, seemingly a recurring statement, but I'd like to thank you all up front for the awesome knowledge base and helpfullness within the forum!

Now, onto my current project....
I have searched, but haven't come across a discussion purely regarding through-hull fittings and water supply issues to inboard engines, speciafically shaft drive engines. I am keen to hear your thoughts and of your experiences.

For two years I/we have been undertaking a comprehensive refit of my much-loved 33' gamefishing boat. Given the numerous issues closely related to engine overheating, and the fact I'm repowering with 370hp versus the old 210hp, I've scrapped every last piece of engineering within the boat and am starting fresh.

All water intakes/pickups/exhaust, everything, sealed up/glasses over/new. The boat is effectively new, and we're yet to drill a hole in it.

Now, we get to chose the water intake gear!
The engines are reman Cummins 370hp. Mr Cummins says 2" intakes are required, so, given the warm water we operate in, I'm giving it 2.5" plumbing and will be routing the plumbing as direct as possible, with minimum bends.

Starting from under the boat.... I'm planning on moving the intakes for the engines closer to the centreline/keel of the boat. The position I've chosen is not detrimaental to prop water flow, nor affected by strakes. A prime position I think.

Previously the intake scoop was the scoop type (picture #1), but I'm considering the style of the second picture (#2). I feel this slotted style as opposed to the also available cheese grater style will lessen the effect of growth. Is there any faults in my thinking? Are these intakes ok for a vessel that (hopefully) spends a lot of time backing down hard on fish?
#3 is a scoop I've seen elsewhere and like, but have been unable to find as of yet. Thoughts on this? I think it may foul with growth easily.

#1


#2


#3


Moving inside, Groco 2.5" full flow ball valves seem to be a "no-brainer", attached to Groco sea strainers, which, despite having what appear to be plastic sight bowls, show a good following by my fellow "The Hull Truthers". Correct? (pic attached).
I have questions here though.
Listed are "non-metallic" which I read as PLASTIC, stainless steel, and Monel basket options.
What is "the choice" for ease of maintenence in my salt water enviroment?
All metals will be fully bonded throughout the boat.



Thank you for your replies in advance!

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Old 03-11-2012, 11:51 PM
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http://www.google.com/products/catal...wAw#ps-sellers

Those are the ones you want. The one that you show wont keep all the crap out... the cheese grater style will... When going with external strainers always go one size larger. If you are adding external strainers, there is no need to put basket strainers inside the hull.
There is absolutley NO benefit (other than the guy that youre buying your valves from's wallet) going to a 2.5", NO benefit, the cummins calls for 2", the water pump only accepts a 2" hose, pointless to go larger. When you install the external strainers, remember nice and close to the centerline of the hull with a slight inward pitch to use the water flow off the hull to your advantage.
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Old 03-12-2012, 12:04 AM
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Thanks for the interesting reply Whaler.

Am I really that far wide of the mark? I thought of the outside strainers more as a way of creating a high pressure zone and directing the water toward the through-hull fitting. Without some form of scoop the water simply rushes past doesn't it?

Are you saying I could do away with an internal raw water strainer if I went to a cheese grater intake? How do we clean them or check them on a regular basis? Go swimming?
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Old 03-12-2012, 02:55 AM
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Originally Posted by Whaler1777 View Post
There is absolutley NO benefit (other than the guy that youre buying your valves from's wallet) going to a 2.5", NO benefit, the cummins calls for 2", the water pump only accepts a 2" hose, pointless to go larger.
But if you DO go larger then the hull will take on significantly (like 2x) the water than with say a failed 2" fitting - so your pumps need to be bigger to cope with the inflow....if you worry about that sort of thing. In general any through-hull should be big enough, but no bigger, than required.
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Old 03-12-2012, 03:18 AM
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My thought process behind going to 2.5" is to safeguard against partial blockages and ensure, without doubt, there is enough water.
I know the pump inlet on the engine is 2", but, surely, if there is 2.5" all the way to the pump, and a step down right at the pump, that simply gives the pump a larger volume with which to draw from, there is no negatives (the cost difference is negligible).

I'm only wanting to discuss it, not argue, but think of it this way.

Manufacturer XYZ's engine needs 1,000cfm at max power for their warranty to be valid. They're not going to deny warranty because your engine room can supply 1,500cfm are they? Sure, it NEEDS 1,000, but 1,500 is great!

Same story with exhaust sizing....

Same for fuel supply capacity....

Why not raw water intake????
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Old 03-12-2012, 03:28 AM
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Same story with exhaust sizing....

Same for fuel supply capacity....

Why not raw water intake????
...because a bigger raw water intake will sink you faster if you have a pipe/valve failure and will bring zero benefit to the cooling system.

Bigger fuel supply won't sink you faster. Bigger exhaust won't sink you unless it involves a bigger through-hull but we are usually above the waterline here.

Just added -partial blockages don't often happen except by neglect (marine life buildup, silt etc), most cooling systems blockages from debris/trash are sudden and will affect a 2" just the same as a 2.5" so unless you want to plan for maintenance neglect you may as well go for the safer, smaller fitting and fit alarms - it will protect better.

No problem discussing, but a disagreement doesn't = argument

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Old 03-12-2012, 03:34 AM
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I didn't mean we were, or about to argue

But, with all due respect, my boats are very well maintained, and the likleyhood of sinking because of a failed skin fitting or below waterline hose/fitting failure (at least on my boat) is so far from reality it doesn't enter my mind.
If for some reason all of my large capacity electric pumps fail, then the manifolded pair of engine driven pumps can't keep up, and the dual Whale hand pumps don't make a difference.... well, I'm stepping up into the raft, because Davy Jones wants it in his locker more than me....
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Old 03-12-2012, 03:35 AM
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Every length of tube and elbow causes a restriction even without partial blockages. Going to 2.5" will help insure that 2" of water is available to the pump.
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Old 03-12-2012, 03:41 AM
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Every length of tube and elbow causes a restriction even without partial blockages. Going to 2.5" will help insure that 2" of water is available to the pump.
^^^ This is my point exactly.
And, as I am doing the new install myself, the local dealer looks hard to find a reason to not sign off on the install (I can hear it now; "too much restriction in your raw water intake mate!").

So, the issue isn't really my choice of 2.5" plumbing, what I'm really asking for is all your thoughts on setups, and brands you've have good or bad service from.
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Old 03-12-2012, 05:39 AM
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We use the perforated hole wedge type as in your 3rd option as well Woo. Buck Algonquin makes them with different size holes which you should pay attention to as well. Engine manufacturers specify what size filtration to make sure they aren't allowing debris into the system that will clog heat exchangers. We always use the removable screens that have holes drilled at an angle that will force water into the fitting at speed and have never had a problem backing down.

We do not use an internal strainer with these units as they do the job externally and fouling of the smaller holes isn't a problem if they are primed and bottom painted properly. What we do is messy but I dip the screen in a tray or pail of slightly thinned bottom paint and gently blow out the holes with an air gun. This is MESSY and you want to make sure you don't do it around anything you don't want spatter coated but it works just fine.

Like you, I oversize the scoop strainer slightly, using a 2.5" when 2" or 4" when 3" is called for and we actually have positive pressure readings in front of the water pump itself so never have issues with engine manufacturers in that regard. I feel the slight increase in wetted drag is worth the peace of mind.
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Old 03-12-2012, 07:45 AM
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the external strainers help re-direct the water to the intake thru hulls, without them water would just be skirting over the through hull.. Again, No benefit whatsoever to having a 2.5 through hull if you are stepping it down to 2.5" totally useless... The odds of the through hull are pretty slim and both would sink your boat just as quickly imho... Make sure youre getting a flanged ball valve and not just a valve.
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Old 03-12-2012, 07:51 AM
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A larger seacock, fittings and hose will afford less restriction / greater flow when keeping the raw water pump as a constant. Here, more is better.

The scoup strainer w/ a removable opening will be way easier to keep clean. Mine lis like the first image, integrated w/ the through hull. It is a butt pain to pick out growth while the boat is floating. The trap door style is way better.
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Old 03-12-2012, 08:17 AM
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I've got the exterior mounted "type 3" strainers only..no interior strainer. After 10 years I've never had sand or junk in the heat exchanger or engine blocks. My exterior units are Sen-Dure, and I don't know if they're still made........
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Old 03-12-2012, 10:36 AM
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I also have the #3 units or similar, and no internal strainers and I have had no issues. I really like not having internal strainers due to the extra work, cost, and complexity at no added benefit. I don't care for the added drag on the hull, but I really don't have a way to quantify that drag anyway. If I was redoing my hull, I actually would not use strainers at all, internal or external.
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Old 03-12-2012, 05:51 PM
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Originally Posted by bills106 View Post
We use the perforated hole wedge type as in your 3rd option as well Woo. Buck Algonquin makes them with different size holes which you should pay attention to as well. Engine manufacturers specify what size filtration to make sure they aren't allowing debris into the system that will clog heat exchangers. We always use the removable screens that have holes drilled at an angle that will force water into the fitting at speed and have never had a problem backing down.

We do not use an internal strainer with these units as they do the job externally and fouling of the smaller holes isn't a problem if they are primed and bottom painted properly. What we do is messy but I dip the screen in a tray or pail of slightly thinned bottom paint and gently blow out the holes with an air gun. This is MESSY and you want to make sure you don't do it around anything you don't want spatter coated but it works just fine.

Like you, I oversize the scoop strainer slightly, using a 2.5" when 2" or 4" when 3" is called for and we actually have positive pressure readings in front of the water pump itself so never have issues with engine manufacturers in that regard. I feel the slight increase in wetted drag is worth the peace of mind.
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Originally Posted by Whaler1777 View Post
the external strainers help re-direct the water to the intake thru hulls, without them water would just be skirting over the through hull.. Again, No benefit whatsoever to having a 2.5 through hull if you are stepping it down to 2.5" totally useless... The odds of the through hull are pretty slim and both would sink your boat just as quickly imho... Make sure youre getting a flanged ball valve and not just a valve.
Quote:
Originally Posted by wingless View Post
A larger seacock, fittings and hose will afford less restriction / greater flow when keeping the raw water pump as a constant. Here, more is better.

The scoup strainer w/ a removable opening will be way easier to keep clean. Mine lis like the first image, integrated w/ the through hull. It is a butt pain to pick out growth while the boat is floating. The trap door style is way better.
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Originally Posted by billinstuart View Post
I've got the exterior mounted "type 3" strainers only..no interior strainer. After 10 years I've never had sand or junk in the heat exchanger or engine blocks. My exterior units are Sen-Dure, and I don't know if they're still made........
Quote:
Originally Posted by BigosS View Post
I also have the #3 units or similar, and no internal strainers and I have had no issues. I really like not having internal strainers due to the extra work, cost, and complexity at no added benefit. I don't care for the added drag on the hull, but I really don't have a way to quantify that drag anyway. If I was redoing my hull, I actually would not use strainers at all, internal or external.


Thank you all for your awesome feedback!
With this, and some very welcome advise via PM from one of my boating idols, I feel confident enough to do away with plans for internal strainers, and go with these;


Now all I need to do is to find out what screen size would be recommended for 370hp 6BT's. Anyone know for certain right off the top of their head?
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Old 03-13-2012, 06:25 AM
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Now all I need to do is to find out what screen size would be recommended for 370hp 6BT's. Anyone know for certain right off the top of their head?
Cummins and CAT both want to see holes no smaller than 3/32" on the strainers. That being said, they both have approved the use of these on our installs. Even though the holes start out at 1/8", by the time you add the primer and bottom coating thickness you are at or less than 3/32".
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Old 03-13-2012, 06:33 AM
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Cummins and CAT both want to see holes no smaller than 3/16" on the strainers. That being said, they both have approved the use of these on our installs. Even though the holes start out at 1/8", by the time you add the primer and bottom coating thickness you are at or less than 3/16".
uh.....3/16" is LARGER than 1/8".......

1/8th plugged up is more like 1/16th.
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Old 03-13-2012, 06:36 AM
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Quote:
Originally Posted by bills106 View Post
Cummins and CAT both want to see holes no smaller than 3/16" on the strainers. That being said, they both have approved the use of these on our installs. Even though the holes start out at 1/8", by the time you add the primer and bottom coating thickness you are at or less than 3/16".
The Buck southbays are very nice, i have them on my bert. The screen is removable for cleaning. B&S also makes southbays, also very nice. However, my only recommendation with the buck is to drill and tap the back for B&S zincs. As the B&S comes with zincs, but no removable screen.
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Old 03-13-2012, 06:38 AM
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uh.....3/16" is LARGER than 1/8".......

1/8th plugged up is more like 1/16th.
Thanks for catching that, second cup of coffee hasn't kicked in yet!
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Old 03-13-2012, 06:46 AM
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I also have the #3 units or similar, and no internal strainers and I have had no issues. I really like not having internal strainers due to the extra work, cost, and complexity at no added benefit. I don't care for the added drag on the hull, but I really don't have a way to quantify that drag anyway. If I was redoing my hull, I actually would not use strainers at all, internal or external.
One of my neighbors tried removing some large 4" Sendure scoop strainers a couple years ago and claimed he picked up early a knot. I thought that was a stretch myself but they were some huge wedges, much larger profile than the same size Buck's.
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