Can a modern boat survive without through hulls?

[altruistica]

I'm completing a 40ft power catamaran. It was originally designed for two 60HP petrol outboards and a roof that can take a 6kW solar array. I'm completing it with two 15kW Aquamot Trend 15.0 electric outboards. Power will come from two 45kWh LiPO4 banks and the liveaboard will be powered from two 11kW, 48V solar inverters. I mention all of this because the power will essentially be 240V, with all the marine stuff (pumps, lights etc) using the relevant 12V or 24V power supplies. The exception is the 24v windlass, where I will use two 12V lead acid batteries in series, backed up with a 240V battery charger.


The tanks which are already fitted feature two 250l aluminium petrol tanks, one 250l grey tank and one 250l black tank. As there are no through hulls on the boat at the moment, for the purposes of emptying the grey and black tanks, could I fit above waterline through hulls, which might exit about deck height on the side of the hulls, to which a trailing section of hose could be added to take the waste under the waterline?



My thinking on this, is that the tanks would probably only need to be emptied once a week perhaps, and would retain the integrity of the new hulls. Is this thinking wise or unnecessary?


The cat has already been Coppercoated with the maximum draft being estimated with the original design, around 520mm (about mid hull position). As I won't really know how the cat will be displaced until she's in the water (my rough calculation is that hopefully she's going to weigh between 4 and 5 tonnes), can a depth sounder device be fitted without a through hull?



Are there other considerations I should be thinking about regarding through hulls?


My boating / sailing experience is very limited, but I envisage the kind of sailing being coastal / island hopping around the Med for at least a few years once on the water so I can see how the solar system performs and what its limitations are.

[pcmm]

What is your aversion to thruhulls? Properly installed (and operated) they pose no real significant increase in risk.

[rslifkin]

It's possible to avoid thru hulls under the waterline, but a properly installed thru hull is low maintenance and low risk, so I wouldn't be too afraid of them. Avoiding them is likely to add some inconveniences. There's no reason grey water can't be discharged above waterline as long as you can keep it from dripping down the side of the hull. Factory sink drains on my boat are all above waterline. Black water would be best dumped below waterline though.

[GILow]

Black water is best pumped out via shore service via a deck fitting. If not, at sea and off shore far enough to be compliant with local laws. In the latter case that means you will almost certainly be under way when pumping out.

Therefore, a black water outlet just above the waterline is fine, it gets rinsed constantly as you are pumping out.

I know this because it’s been my setup for six or seven years now. Works just fine.

[ranger58sb]

Reverse cycle AC -- for air conditioning and heat -- are usually fed raw water via a thru-hull under the water line (with seacock and strainer following).

If you might ever want that, properly installed thru-hulls are safe enough.

-Chris

[UnicornUnicorn]

Hi Altruistica

I agree less thruhulls less risk in general terms.

dont forget that normally a drive shaft is a through hull
also a rudder shaft is usually a through hull
sailboat keels normally are trough hulls :-)

hard to escape those ones
everybody have a great one!

MV Unicorn

[SailingHarmonie]

Interesting boat.

I'm very curious about how you expect the power numbers to work out? What will be your crusing range and speed? How long to recharge by solar alone? I assume you will have a shore power fed charger for the main battery bank? If the boat was designed for 60HP engines and you will be using 15kW electrics, that is a significant reduction in top speed. What speed do you expect?

I agree with thruhulls comments above. Gray water is easily discharged above water level whenever needed. Black water is best discharged below waterline, but if you are willing to put up with the hassle and mess of another approach it can work. If you have no need ever for air conditioning then you can skip bringing water into the hull for that. Most modern boats are aid conditioned, especially catamarans which can act like little greenhouses and get REALLY hot in the sun. Air cooled units are inefficient, bulky and noisy. I would happily swap all those issues for one thruhull.

BUT... you have an irrational fear of thru-hulls. Properly installed and qualtiy thru-hulls do not fail. What fails is the hose connected to them. Keep the seacock closed when not in use, and your risk is so near zero as to be not worth worrying about.

Boats sink from "thru hull failure" in one of two ways. At the dock when a hose fails, and nobody is there to close the seacock. Or, at sea. Someone notices that the bilges are filling fast, and before the crew can identify and close the leaking circuit, the water has risen high enough to make that impossible.

The lessons here are:

1. Close all seacocks when leaving the boat or not in use.
2. Minimize the number of seacocks and make SURE that each one is easily accessible in an emergency.

Lesson #2 above is routinely violated in production boats. Sometimes to extremes that would be laughable if this was not such a serious design flaw.

[PJS]

Originally Posted by SailingHarmonie

Interesting boat.

Lesson #2 above is routinely violated in production boats. Sometimes to extremes that would be laughable if this was not such a serious design flaw.

AMEN to that comment. I cannot believe boat builders are/were permitted to get away with some of the placements that I would consider a safety hazard. I have to do boat yoga to get to my main seacocks on a good day. If I ever had to close one in an emergency, I'm not certain I could do so. Scary proposition.
Assuming the engine compartment doesn't flood and the lift actuators continue to work to lift a 300+ pound engine hatch that takes almost 3 minutes to open....
My greatest fear.
Needless to say, my seacocks are inspected regularly, serviced every haul out and hoses and clamps replaced before they require.

[thinwater]

A cat can also do something most monohulls will struggle to do: All of the thru-hulls can be in bulkheaded compartments.

On my PDQ the thru-hulls related to the head and speed sensor were in one small buklheaded compartment, that also served as a bow crash tank, and the through hulls for the ACE were in the other crash tank. In fact, the speed sensor was put back incorrectly after the sea trial, pinching an o-ring, and the compartment flooded during our trip home. In stead of a crisis, it was a simple matter of some pumping and applying Vaseline.

If you are concerned, put them in a crash tank with a deck hatch. Easy.

[altruistica]

Thanks for all the replies.
My aversion to thru hulls is simply that it's a hole in the boat. That's great that the grey tank thru hulls are normally sited above the waterline. I think I'll do the same with the black tank ones too. The toilets are electric Jabsco ones which macerate and use fresh water.


I've read different countries have different laws regarded macerated waste as opposed to non-macerated. I've already installed an electric air con unit (this one) which draws 700W per hour on full and half that on an economy setting. Because the saloon roof is almost totally covered with panels, I'm expecting them to give the roof shade in hot climates. The front, back and sides will still allow lots of heat inside, but only time will tell.


I'm finishing the boat as the original builder envisaged, a kind of houseboat with outboards. The only difference is the outboards and if they don't work, then the fall back position is simply installing two petrol ones. It all depends on sea state and wind as to what kind of numbers the system will produce. I'm finding with modern panels, they actually can produce more than their spec'd amount, up to 30% more. My solar inverters should easily manage any over production. I'd expect the motors to produce around 4-5 knots using 1.5kW per hour, but it all depends. Just like a diesel engine, a 30HP engine will behave massively differently with differing conditions.


The cat is a Richard Woods designed Skoota. The hulls remind me of Warram hulls as at the widest point, they are only a double bed wide so this should make a difference cutting through the water as opposed to some 40ft production cats. All this is new to me, so I only know what I've read. The solar part (panels, batteries and AC production) isn't new as I installed a whole house system a couple of years, would you believe it with a 92kWh lead acid battery bank (they were cheap and lithium at the time, wasn't).
I'm expecting to be able to sail 20 miles (coastal) with full batteries in most conditions that I would want to venture out in. With solar however, you obviously have to guage your day with conditions. If the sun's out, then the washing machine can go on, if not, then save it for another day.



Interesting idea about the crash tanks.


The original builder has built the bows like this, filled with the correct kind of foam.


I'm finishing the transoms and it seems he had a similar idea with one of the compartments at the rear. If I installed a speed / depth sensor like

this one

I could build a small compartment. If I were to ground the cat

like this

, I would have to make sure the sensor couldn't be damaged by doing so.


Is there any speed / depth sensor that just sits on the water, or possibly could be attached to one of the outboards?

[donradcliffe]

Many boats are equipped with depth sensors that work through the hulls. The only drawback is some loss in range.

[NorthCoastJoe]

You could go with a sea trunk, that is one thru hull for all sea water intakes tapping off it.
One valve at the hull level and individual valves tapping off the sea trunk for their various uses.

In an emergency one valve shuts down all intakes. You could do the same for all
waste water. So then two thru hulls in the entire boat.

[deblen]

Easy-just install seachest(s) with top of chest above waterline.


They are commonly used for scanning sonar hoist tubes in seiners.


https://www.captainchrisyachtservice...ea-chest-envy/

[NevilleCat]

I didn't read if your hulls are cored or solid glass...if wood or foam cored a depth transducer won't shoot through as it would if it were solid glass.
However given that it's a cat you should be able to use a transom mount transducer that will probably come as part of your chart plotter/ fish finder package. You might have to experiment with placement to get the least disturbed water flow.
I think that's another advantage of cats; on my last outboard powered sailing cat the only below waterline through hulls were for the toilet, which you have probably solved.

[Cpt Mark]

On my cat, in the engine room on the inboard side of the hulls there are various through hulls for discharge including waste water, black tank emptying etc. Grey water from sinks goes straight down. All discharge above the waterline and none lands on the hulls.

I wish mine had been built with a sea chest or whatever. I dislike strongly seacocks in places where the are difficult to get to let alone service.