1" Strainer for a 1 1/4" hose and intake?

[WindLove]

I am having my engine raw water cooling system refurbished for a new engine.

The new engine's seawater intake is 1 1/4" but currently I have a 1" seacock. The boatyard told me I have to replace the seacock with a 1 1/4" to accommodate the larger hose, but then said it is fine to continue using my existing 1" Perko seawater strainer.

That seems strange to me. If I need to change the seacock, why would the 1" strainer be acceptable. Wouldn't it restrict the flow, or does it not work that way?

[Paul Annapolis]

All good questions, so perhaps a call to the engine manufacturer will help. My hunch is that flow is not a problem. I hope someone else on here can help. "There is more to heaven and earth than is dreamt of in your philosophy..."

[sailorchic34]

What is the HP of the new engine??.

[Paul Annapolis]

HP likely has little bearing in this situation as I would think that engine block size and marinization of the engine would be more of a factor but in any event, horsepower would likely only go up or down a very small amount when replacing a sailboat engine and may not affect pumping capacity much either...that's my hypothesis...anyone else have ideas on this one?

[boatman61]

You should be able to braze a collar to bring it up to 1 1/4"size..
Most plumbers merchants should stock a suitable brass/bronze/SS fitting.

[Cheechako]

1" is likely fine for your new engine. My 80hp had 1". You will just a have bit higher velocity in the hose pre pump is all. You should be able to find a 1/1.25 barb nipple. Assuming your intake is well below the waterline, the water will squirt out of that open seacock like a big garden hose!... much more than your engine wants.
The other consideration is what type of seacock. Some will have a 1" bore and some have a tiny bore compared to the rated size. I found this in Ball valves. Some are rated by the size of threaded ends, but the bore is not that size!

[Stumble]

What size does the engine require? There is no downside to oversizing the strainer and thru hull, but one that is too narrow can be a major issue.

Without knowing the recommended size it's impossible to tell you if what you have is suitable. You may need 1.25 the whole way, or leaving it as a 1" may be fine.

[HopCar]

I'd match the whole system to the size of the pump. You don't want to restrict water supply to a rubber impeller pump. Aside from the possibility of over heating the engine, the impeller will not last as long as it would if it was getting all the water it needed.

As Cheechako pointed out, when buying valves you want to look for full flow valves.

Since you're working on the intake system, you might take the opportunity to rig it so that you can use it as an emergency bilge pump.

I'd love to quote you on the parts you're going to need to make this change.

[sailorchic34]

Originally Posted by Paul Annapolis

HP likely has little bearing in this situation as I would think that engine block size and marinization of the engine would be more of a factor but in any event, horsepower would likely only go up or down a very small amount when replacing a sailboat engine and may not affect pumping capacity much either...that's my hypothesis...anyone else have ideas on this one?

Ah, HP has everything to do with it. More HP requires more heat rejection. So knowing the peak HP/KW produced, allows for the calculation of the heat rejection required and the amount of cooling water required. Basic engineering.

Odds are 1" would work. But it depends on restrictions in the system and the length of pipe and or hose to the suction inlet to the raw water pump.

Hopcar raises a good point in that not all 1" valves are 1", also called full port. A regular, not full port ball valve will have about a .85 inch diameter port. where as a 1" full port ball valve will be 1" diameter.

[WindLove]

Sounds sensible to me. I think much bigger engines have 1 1/4" intakes, and mine is only going to be 47 hp. I don't even see why I need a 1 1/4" seacock. It's not free.

[HopCar]

That does sound like a big pump for such a small engine. I have a 210 hp Cummins with an 1-1/4" pump. I wonder why the manufacturer would install such a large pump on an engine that small?

[sailorchic34]

A 47 bhp engine will produce 120mbh of energy. A diesel engine is roughly 50% efficient so roughly 50% of the energy is wasted as heat, the other 50 percent is converted to motive power. So about 60MBH is heat to the walls. That at 20 degree delta would require 6 gpm.

Even if the whole amount of energy was wasted as heat and allowing it all to the engine walls, it's still only 12 gpm at 20 degree delta. That's probably a low delta. I suspect most engines are running 30-40 degrees delta on raw water, based on hose temperatures prior to the mixing elbow.

Even at 12 gpm, a 1" diameter hose will have about 2.1 feet of head loss per 10 feet of hose length. That is very doable for a 1" hose and is not excessive at all.

So short answer a 1" hose will be fine from a flow rate standpoint. Assuming you have less then 10 feet of hose total to the pump and heat exchanger and aft loop.

So run 1-1/4" hose to the discharge of the seastrainer as reduce down to the 1" port connection. BTW hard pipe pressure drop is much less then hose. Partly due to the soft rubber liner that has a higher friction coefficient then smooth metal pipe.

If you have a 1" full port seacock, your probably good. If you had a long run of hose (more then 15-20 feet total for all hose used) then changing out the seacock to 1-1/4" would be safe. For the typical short run it's probably not an issue.

One issue with a 1" seacock is you would want to make sure the seacock had little hard growth. To many critters at the seacock would reduce the flow rate, or rather increase the pressure drop. That would be one reason to install a 1-1/4" seacock as it give you a bit of a safety margin.

[HopCar]

Sailorchic, I really don't understand a lot of what you just said, but I love it when you talk science.

[Marqus]

Originally Posted by sailorchic34

.... BTW hard pipe pressure drop is much less then hose. Partly due to the soft rubber liner that has a higher friction coefficient then smooth metal pipe.

Good post.

When you say "much less" in the above quoted sentence, can you put a ball park number to it - eg. for typical boat plumbing (copper or iron pipes vs car heater style rubber hose) is it typically something like 20% less or more something like 80% less pressure drop?

[sailorchic34]

Originally Posted by Marqus

Good post.

When you say "much less" in the above quoted sentence, can you put a ball park number to it - eg. for typical boat plumbing (copper or iron pipes vs car heater style rubber hose) is it typically something like 20% less or more something like 80% less pressure drop?

Roughy 150% or more pressure drop in hose then for metal pipe of the same size and length.

For example 1" hose flowing 6 gpm will have a pressure drop of roughly .18 psig per 10 feet. 1" schedule 40 steel pipe flowing 6 gpm will have a pressure drop of 0.12 psig per 10 feet.

At 12 gpm 1" hose has .9 psig drop per 10 feet. 1" steel would be 0.45 psig for 10 feet. Note that hose barb fittings increase friction loss as they restrict the diameter. Steel and copper pipe fittings on the other hand are same area as the pipe.

Brass or copper would be slightly better then steel. Hose has a rather high friction coefficient.