Through hulls on passagemakers ???

I understand your reluctance to drill holes in the bottom of a perfectly good hull, but a properly installed and maintained thru hull will not sink you.

In fact, I would be willing to bet that of the millions of thru-hulls installed on boats, both correctly and poorly, compared against boat sinkings, that the thru-hulls were responsible a very small number of sinkings.

I think I would sleep very well on any Nordhavn,

Steve

 

That's why Michael said put the seachest in the engine room and make that a water tight compartment. I agree. If it leaks, it won't sink you. Also being able to use the cooling pump on your engine as an engine room bilge pump is a good precaution. Set up with valves so the engine can be switched to suck out the engineroom and pump it overboard. In emergency.

 

60mm is about the largest practical thru hull on a small craft. A 60mm valve is a big boy. Flange to flange ball valves are the most compact , easiest to service and install. Well painted steel ball valves are cheaper and when properly installed give a good service life.
I never have much luck with gate valves and only use then when space is very cramped.

Be aware that many pumps are not self priming and need sea water pressure to operate correctly. Dont locate your seachest outputs too high.

 

If you have a seachest the starts leaking, it should be just that, a leak. And you would address it like any other leak on what ever type(steel, frp, wood ect.) that you have. There would be nothing to take a hit on the bottom of the hull, and a stout screen. But, if you run aground or hit a deadhead just right, you sure could have a large problem. The owners whom i have spoken with all have them in a bulkhead sealed engine room.

 

Best to scetch your proposed sea chest.

As a filter go fine and large surface area. The troublesome debris in water is sea grass. If it snakes thru the filter screen, then enters the engine cooling system, sooner or later you must disassemble and remove it. Normally a several hour, on you hands and knees, job.

On a proper sea chest you should be able to shut off the thru hull valve and pump the sea water out of the sea chest before opening the chest.

The goal in life is to never allow one drop of sea water to enter the engine room bilge.

 

"H" layout thru hulls....two sea strainers ontop of two valved standpipes...feeding a distribution manifold is worthwhile. You can Isolate port side to clean while running off starboard side.

 

Off the shelf engine pump bypass for bilge:

http://www.groco.net/00-scks-valves/sscv.htm

Steve

 

Not wise to use bilge water to cool an engine during a flooding incident.

the bilge strainer clogs, Engine cooling fails and youre up the creek without a paddle.

Special twin chambered vane pumps are used . Chamber one is the seawater engine cooling...chamber two is a full time scavenge bilge pump. The second chamber is always pumping the bilge, it may run dry and not burn up because it is cooled with seawater from the engine side chamber .

Stiemel of Germany makes this common twin chamber pump.

 

Always surprises me when I see Nordhavns hauled out. Once counted 14 thru hulls at or below the waterline. And these are marketed as passagemakers, sure, I guess, but you'd think there would be a better way.

 

Learned a lot about sea chests...and I as well have seen Nords out of the water and was shocked at the number of thru hulls.

Kept the formula from a university website,a rough idea and a smooth hole.

GPM=20 x (Diam." x Diam.") x square root of feet depth.

So a 2" hole at 3' is about 139 gpm and 6' down is about 192 gpm.

A 3" hole at 3' is 311 gpm and let's say for ideas,6' is 432 gpm.

And as your boat sinks,the hole gets deeper and gets even more pressure and flow.

That imaginary 3" hole at 6'/432 gpm..if your boat sinks another 5' then it's at 11' and almost 600 gpm is getting in.

 

Use only bronze thru hulls from a well known manufacturer NO PLASTIC

 

Most boats sink in their harbour when there is no one aboard and it’s not thru-hulls but the hoses and connections.

It's sensible to keep the thru hulls to a minimum, check the seacocks at haulout and check the connections from the seacock on. I have never heard of a failed sea cock unless it's terribly neglected..

The nicest aspect of a large single valved standpipe or manifold assembly is being able to find all the feeds in one location I wouldn't worry about a sea cock or stand pipe falling off either if it’s properly constructed.

In calmer weather ( but never in rough weather) you can easily plug an individual thruhull from the outside even a large round pipe can be plugged with a bung. You can mark on the gunnel where thruhulls are located. But the only time a seacock might be broken off is if heavy equipment starts flying around, you can provide good protection for even a plastic seacock. You can also build a watertight box around a seacock if you are really paranoid.

But there are other important factors eg bilge alarms.
What are the pumping capabilities, the little 12v bilge pumps are a joke. Do you have access? A bucket brigade is very effective but seldom practicable. Manual pumps are pretty useless on larger vessels, A portable petrol or diesel driven pump is a good option on a larger craft as are genset powered pumps run from an emergency circuit. Remember the ELCB’s will trip for the regular circuits at the first dose of seawater.

The idea is to stem a major leak as much and as quickly as possible so early detection is paramount and the pumps usually fight a loosing battle until the flow is reduced by prompt action.

I’d be more concerned about transducer thru-hulls and prop shaft seals than seacocks.

 

That's why my transducer is in a sea chest and my prop shaft is oil filled with seals on inboard & outboard ends.

As for through-hulls, I put in a 2" intake with a flange to bolt on a ball valve and I have 2 below the WL discharge lines, also welded steel flange fittings. They may block but nothing is going to break them off from an inside impact unless it's also capable of literally tearing the 4mm hull plate.

The intake is going to an internal sea strainer and then manifold off for the delivery lines. A blockage means shutting the valve, taking the top off the sea strainer, cleaning it out and putting it back. Not a perfect solution but good enough for me.

People talking about engine rooms with water tight bulkheads are talking about big vessels. Name me 1 boat under 20m built like this....

PDW

 

I am overwhelmed with good ideas. Sounds like an easily solvable issue(assuming i am smart enough to buy or build a boat with a large enough engine room) and one that can be adapted and even be modified to fit different problems in different parts of the globe. The diesel ducks are the only smaller boats that come to mind that have 3 watertight bulkheads, with the engine room being the middle one. As for thru hull numbers on smaltt(60' and under), so far my investigations find one Nordhavn owner that admits to having around 30 separate thru hulls. I do think i want a boat that performs that many functions, whatever they are???

 

He's got to be counting above the waterline thru hulls in that tally, which I don't think should be a consideration.

Steve