External clamshell water inlets.....

[Genesis]

I am seriously considering removing the grate tines in my clamshells for the main engines.

I pulled them when I came out this year, and took 'em back to the house. They were full of internal oysters, which you CANNOT get to through the tines, and layer upon layer of bottom paint, which was restricting the water flow.

Here's the thing - I have internal strainers. So why do I need the external grates - what purpose do they serve?

This much I know for certain - I can't get up in there to clean them in the water. No way, no how. And I've always had marginal raw water flow - which I attribute to the restriction, even with the "ram effect" of the clamshells.

Anyway, I'm just wondering what everyone else's thoughts are on this. I've got a regular "grate" style one for my genset and AC system, which are reasonably clear and ok. My livewell strainer was completely plugged though - it came off and came home.

All of these got the brass wire wheel treatment, and look much better now, although not COMPLETELY clean - but certainly servicable as they now sit.

Do those tines really do anything for you or are they just trouble and something I should considering cutting out?

 

[Nick]

Karl,

I have the wedge shaped external strainers with the removal brass screens. The screens have small dia holes about 1/8 in or so. I remove the screens and wire brush the holes every spring. I also run the brush up the intake and there is not usually any growth (one or two barnacles). I also get a fresh coat of antifouling paint in the intake. Two years ago I installed new internal Perko basket strainers and decided to leave the external ones in place because we encounter weed (eel grass in this area in the NE) and the external screens keep the stuff out of the intakes entirely). In practice I would rather have the weed, or whatever, work its way to the internal strainers where I can remove and clean it in the boat. What I found several years ago in a gas powered boat with the open grate intake scoops is that the weed was pulled into the seacock and then jammed in the grates and in the seacock, the elbow connected to the seacock and the short piping upstream of the basket strainers. I quickly started running warm then hot. Pulled the internal baskets and there was hardly any weed. Pulled the intake hose, very little water flow. I snaked a hangar wire through the intake as best I could with the grates in place and pulled hand fulls of weed. Same problem in the P&S engines and the generator intake. When I hauled the boat I had the grates cut out of the intake scoops and it eliminated the problem. I would assume if you have simple connections with few or no bends between the intakes and the basket strainers, and no weed problem in local water, then I do not see the benefit of the external strainer.

Nick

 

[MikeP]

Both of our 53's engine RW intake clamshells have two of the tines removed. It was obviously done intentionally by the previous owner since they are the same two tines on both intakes. With two of them removed, you can work various tools into the intake to clean it so I assume he did it for the reasons you suggest.

I have to admit that I can't really see why he didn't just remove them all. But I suppose having some of them could still help stop some objects from being pulled in.

 

[Capten]

What about keeping out debris such as a plastic bag?

 

[Genesis]

That's the trade-off I'm trying to get my arms around...... I'm not sure the tines WOULD keep a plastic bag out - it is likely to go right between them and up the intake anyway!

 

[Maynard Rupp]

Karl...I found ours almost closed from the previous owner's 17 years of bottom paint. I took them home, stripped them, and sandblasted the scoops. Put them back on with 4200 as the screws go through the hull. When we pulled the boat last fall they were like new. We don't have barnacles of course, but our marina has enough floating seaweed to walk on. I do have to clean the strainers weekly, but the weeds seem to make it through the grating, seacock and lodge in the basket of the strainers. I think the factory spread on the scoops might be OK if there is no bottom paint closing the gaps.

 

[Capten]

That's the trade-off I'm trying to get my arms around...... I'm not sure the tines WOULD keep a plastic bag out - it is likely to go right between them and up the intake anyway!

Possibly but I think you have a better chance of keeping it out with the clamshell - especially large/heavy plastic and especially if you are underway as the wedge shape may help push it away.

I have had good luck cleaning barnacles out of those grilles with a hose removal tool (like a big dental pick). I do it when we are on the hard and it takes a little time but seems to work well.

It would be interesting to see what the newer boats do. My guess is that they have clamshell grilles but then again they probably have to since most of them don't seem to have internal strainers anymore.

 

[REBrueckner]

I recently saw intake strainers with removable pinhole grille/grates. They may have been Groco. The pinhole grates are stainless and can be removed via a few studs. They looke really nice.

I prefer pinhole style over slotted style external strainers because individual openings are smaller and this limits what can be sucked up inside. The surface area is increased to offset the smaller holes and this reduces the intensity of interior light. Removing external strainers is not something I'd do. For one thing it will let even more light in the intake and that promotes more marine growth.
If eel grass or other floating seaweed is present it will generally not be pulled up thru pinhole style, but does get tangled in slotted style. so when your engines shut down, the slotted style will hold some grass..it builds up over time...not so with pinhole style. Eel grass will also build up in interior strainers.
With the pinhole style external strainer, you need to be sure the bottom paint is not slopped on and holes blocked....they need to be cleaned out every year or two....

 

[SKYCHENEY]

I, personally, would try cutting out the tines. If my cooling was so marginal that I was constantly worrying about temperatures, I would really consider trying it. You might also add the raw water flow alarms too, so that if you suck up a plastic bag or something, you will be alerted right away. With those in place, what is the worst that can happen? If you contiually have problems of reduced flow without the tines, then you have to purchase new scoops.

 

[Traveler 45C]

Gen,

Here’s the hull strainer we discussed on the phone:

http://www.westmarine.com/webapp/wc...4&resultCt=1&catalogId=10001&ddkey=SiteSearch

 

[Genesis]

Yeah, my buddy has the strainer type (SS plate that fits into a housing and is easily removed.)

I LIKE that picture! Hmmmmm...... now I've got something to think about here.....

I think I'm going to just cut away the center tines this time around - but if I have problems with things getting sucked in, it'll be time to completely re-think and re-do that part of the induction system, and maybe I'll go for those monster cleanable scoops - certainly they'll shove a LOT of water into the intake at speed!

 

[captddis]

The scoops help to scoop water into the thru hull. Ever notice sea strainers that leak at speed and not at the dock? They insure more flow than you need. I have seen boats with just a few blades left on the impeller that were able to run slowly due to the water being forced in. As far as the Southbay strainers { the wedge } They are fine, the only problem I have seen is if too much paint gets rolled over the holes it restricts flow. All the New Jersey boats do not use main engine strainers only the wedges. Personally I would keep the strainers . Maybe your temp creep will go away now. I have fought temp creep more than once and found growth in the thru hull that was not easily visible until the scoop was removed. I also always install my scoopsmyself. The yards always strip the holes.

 

[Genesis]

Oh I have NO intention of removing the scoops! That's guaranteed trouble; I'm well-aware of the issue there.

What I'm considering doing is removing some of the TINES, not the scoop itself.

And, if necessary, I'll go to BIGGER scoops - which will scoop more.

Thing is, high-output Detroits have ALWAYS been marginal on their cooling. Always. Its a perennial problem and Covington (who packaged up my engines for sale to Hatteras) didn't do anyone any favors by putting the gear cooler on the SUCTION side of the pump - that's a huge engineering no-no (they're called "pumps", not "sucks"), but they did it, and fixing that is damn near impossible due to hose routing issues. This literally DOUBLES the suction vacuum across the gear cooler - I've measured it - and that's with the gear cooler spotless CLEAN having just come back from the radiator shop!

This may be ok in 40F water off Long Island, but it doesn't work when the water temperature is in the mid 80s - like it is around here in the summertime.

The only fix I can come up with would be to run the gear cooler through the heat exchanger (there's a secondary core there which can be used for this) BUT everoyne I've talked to has cautioned that this core is unlikely to be able to maintain the gear oil within safe limits under load - that would be very, very bad..... another possibility would be to find a combined fuel and gear oil cooler to go where the fuel cooler is now - I've done some preliminary investigation on this without much joy.

Anyway, anything that improves raw water flow can only be good...... I'd love to completely re-engineer this system but its non-trivial due to the lack of off-the-shelf parts necessary to do so......

 

[captddis]

I am not going to argue , but I have had two 1985 45 C s with the 6V92 500 HP engines that I have maintained and they hold 180 degrees in the Gulf of Mexico. My 650 HP 8V92s have the same size exchanger and run 170 at 2000 and will hold 185 at WOT in summer. also in the Gulf.

 

[Nick]

Karl,

Just curious, what size intakes and sea strainersdo you have in the boat? (6V92s right?)

Nick

 

[Genesis]

They'll hold 180 if everything is scrupulously clean in the summer. Summer meaning middle of August, 100F outside and 86F water. Our bays can hit nearly 90F during the summer - its nearly a HOTTUB over here.

The problem comes when they're not. There is just no margin in the cooling system on those engines. If you ran at 185F, you were out of cooling capacity - the thermostats are completely open at 185F which means there is no more capacity available - that's not good. I consider anything over 180F to be too darn hot, because I want some margin remaining in the event I have to run on the pins for some reason in an emergency.

Of course right now I can run at any speed I'd like and not have any problems at all - the water is in the upper 50s to mid 60s (depending on where you are) right now....

If you didn't have the gear cooler on the suction side then there is no issue at all. The problem is the pressure drop across the gear cooler due to its open area .vs. pipe size (the hose feeding it is 2-7/8" - big stuff) - its very, very easy to measure this by hooking up some vacuum gauges and going for a run. Jabsco publishes a specification on this, and every 45C I've seen with the setup I've got just barely meets that spec - with a just-cleaned system. Get a bit of crud past the strainers or growth in the gear cooler and you will not meet spec.

There is a fifty percent loss in raw water flow from zero1 restriction to the maximum intake restriction spec for that pump (!)

Covington went to the rear gear cooler (so they told me) because they could not meet the maximum gear oil temperature spec from Allison under full load with the "M" gears. Unfortunately in doing so they violated a cardinal rule of pumping systems, which is that the suction side must be unobstructed to the greatest extent possible.

Avoiding having to tear down the entire raw water system every year to keep creep problems from showing up in the middle of summer would be nice.......

I have to check the pipe size on those strainers, seacock and through-hull - the hose feed to the gear cooler and pump is 2-7/8" - I believe this corresponds to a 2-1/2" pipe size but have to measure it to be sure.

 

[ADaily3224]

Karl,

I have much smaller engines than you, 350HP Cat, but the strainers are very large. They are the pinhole screens, about 10" wide and 22" long. My engines were installed in 1996, apparently this was the preferred method. There are no internal strainers, this worried me, we have surface floating sea weed in fresh water that gets into everything. No problems with these, as said previously, there is so much surface area that water seems to flow easily. The sea weed problem is such a nuisance that I had to put an internal strainer on the head intake. The AC and the generator have the old fashioned scoop with internal strainer and they require regular maintenance and clog occasionally.

Tony D

 

[Capten]

In order to keep our 8V92s cool in the summer months we drain the 50/50 coolant mix and run straight water with Nalcool additive. This was J&Ts recommendation and we have done it for the 12 years that we have had this boat. The Detroits are hard to keep cool but this helps.

 

[Genesis]

It does help, but its also a hassle. I prefer to run the 50/50 mix if I can - yes, I know it has a bit less cooling capacity, but IMHO you shouldn't be that close to the bloody stump of what WAS your engine in the first place!

The "high output" Detroits have always been light on cooling system capacity. The original design on the 6V92s was for ~350 HP, and at that rating there's oodles of extra headroom. At 500..... no.

It just pisses me off to no end that Covington further cut into what was already a bad situation. It would not have been impossible for them to come up with a combined fuel/gear cooler, put it where the fuel cooler is now in the system, and not had the issue arise - ever - but they didn't. Instead they took a way out that totally ignores every principle of engineering when it comes to pumps.....

10x22 wouldn't have this problem I suspect. My external clamshells are ~11x8 - big, but not enormous. The larger the "scoop" the more positive pressure - and better flow - you get when under way, especially when on-plane - where you need the cooling capacity most.


Oh well.....

 

[Top Shelf]

Good idea about removing a couple of tines off of each clamshell. I was under the boat this weekend and noticed some oysters or shells growing on the inside of the clam shell. Was able to break them up, fished some out through the tines, and then picked up the balance (I hope) by flushing the Strainer several times. But what a PITA underwater. Originally they were a pretty good match to the ID of the thru hull!!!

What would you use to cut a couple of tines underwater....got another 10 months or so on the haul out. Thx.