How safely can large catamarans dry out?

[Greenheart]

I was reading an old cruising thread elsewhere...sorry I don't have a link to it. But it raised the point that lots of people dream about the versatility of quite large catamarans being conveniently beached, and safely left to dry out in beautiful locations which are inaccessible to almost all other yachts...

...and the suggestion was clearly made that some catamaran builders are keen to promote this image of large cats being easily dried-out in idyllic spots, whereas doing so may actually endanger the vessel's structure, not only because of obvious risks like occasional rocks on a sandy beach holing the hull, but because big cats require carefully-judged placing when drying out, as their structural stiffness may be compromised when all the vessel's weight is only supported on three corners.

I'd be interested to read owners' accounts of drying out in catamarans over about 35ft - particularly if these stories demonstrate or disprove the claimed danger.

 

[prv]

Coming down on a rock is a legitimate concern, but If a catamaran needed level support across a perfectly flat beach, I'd worry about its ability to withstand waves at sea.

Pete

 

[RichardS]

I was reading an old cruising thread elsewhere...sorry I don't have a link to it. But it raised the point that lots of people dream about the versatility of quite large catamarans being conveniently beached, and safely left to dry out in beautiful locations which are inaccessible to almost all other yachts...

...and the suggestion was clearly made that some catamaran builders are keen to promote this image of large cats being easily dried-out in idyllic spots, whereas doing so may actually endanger the vessel's structure, not only because of obvious risks like occasional rocks on a sandy beach holing the hull, but because big cats require carefully-judged placing when drying out, as their structural stiffness may be compromised when all the vessel's weight is only supported on three corners.

I'd be interested to read owners' accounts of drying out in catamarans over about 35ft - particularly if these stories demonstrate or disprove the claimed danger.

Not sure what you mean by "three corners" but my 40ft cat has keels with a flat bottom to the keels probably 4 or 5 inches across and that flat area is 20 or 25% of the total hull length so the cat can stand on its keels and does when being antifouled. The rudders are shorter than the keels.

Of course, for longer periods it is recommended that the hull is also chocked fore and aft below the bulkheads.

Richard

 

[tcm]

I was reading an old cruising thread elsewhere...sorry I don't have a link to it. But it raised the point that lots of people dream about the versatility of quite large catamarans being conveniently beached, and safely left to dry out in beautiful locations which are inaccessible to almost all other yachts...

...and the suggestion was clearly made that some catamaran builders are keen to promote this image of large cats being easily dried-out in idyllic spots, whereas doing so may actually endanger the vessel's structure, not only because of obvious risks like occasional rocks on a sandy beach holing the hull, but because big cats require carefully-judged placing when drying out, as their structural stiffness may be compromised when all the vessel's weight is only supported on three corners.



I'd be interested to read owners' accounts of drying out in catamarans over about 35ft - particularly if these stories demonstrate or disprove the claimed danger.

I had 49ft french-built cat, and dried out no issues in various places, not a problem, and def wouldn't have any issues drying out on a beach or on a vaguely level (or even not so level) spot, yeah, big rocks permitting ... but really, you wouldn't choose a big cat in the UK that much (i never sailed mine to the uk in nearly 7 years) - they're not much fun for weekend sailing and they're hands-down winners at the long distances and liveaboard thing and that means sunshine, palm trees and blue water. And heh, there's not that much tides everwhere except around UK.... i dried out on the tides in Fiji frinsance, on a launching ramp, quick anode change. Every other time ashore has been on own keels - some yards like to put props at each end but i am pretty sure it didn't need it.

To address your issues, any big cat had better not need "carefully judging"when put ashore due to rigidity or structural issues - cos with big sails in biggish seas they'll be leaping about kerash all over the place. A v experienced mono sailor in big sea on my cat said he lay in his bunk and thought jeez, that was a loud bang -we've hit something! ... but then no shouting or anything so probably not hit something... but then a minute later ... surely that next loud bang meant we've hit something? And so on. So i reckon they should be fine put on any flattish surface free of massive rocks, tho not dropped of course.

I suppose the nice thing about drying out is that the boat is lovely and flat calm. However, catamarans are like that most if not all of the time at anchor

So the drying out isn't a big thing cos you wdn;t much be in tidal waters, and it's flat at anchor. But the drying out is no issue structurally - or def shouldn't be!

 

[bigwow]

Works for me:encouragement:

 

[lw395]

The flip side is that some racing cats are not designed to take the ground at all.
Round bilge hulls not designed to take point loads.
Quite different from a cruising cat.

I guess in between, there are a lot of one-offs which might need thinking about.

 

[Adonnante]

It depends on the design, with fixed rudders and daggerboards damage would almost certainly occur but many cats with lifting boards overcome this by having lifting rudders, as with many of Richard Woods designs. Wooden wear trips bonded to the hull will reduce the likelihood of damage. Cats with fixed keels and rudders are usually designed to take the bottom safely, wooden shoes bonded to the bottoms of the keels are common, mine have been on for 15 years and have only suffered damage needing repair once in this time. I take the bottom on every tide, into mud and dry out over a tide 5/6 times a year. In addition 4 months are spent ashore every winter without and props or support and the cat is stiff enough after 28 years to need a wedge under one end of the keel to stop rocking. Any cat that needed additional support for structural reasons I would not be happy sailing offshore.

Peter

 

[Greenheart]

Gentlemen, I thank you for your sense and insight. I can indeed see that the motion at sea will mostly be more violent than anything the hulls encounter while drying out - although I think the thread I'd read earlier was mainly concerned with sustained loads, twisting the bridgedeck exaggeratedly for long low-tide periods where it meets the hulls.

...really, you wouldn't choose a big cat in the UK that much (I never sailed mine to the UK in nearly 7 years)...And heh, there's not that much tides everwhere except around UK...So the drying out isn't a big thing cos you won't much be in tidal waters...

Thanks for your assurance overall, but I reckon quite a few biggish catamarans are owned by folk who sail predominantly in UK waters, for whom drying out is an issue!

 

[Garold]

I had a Lagoon 38 for couple of years and a Lagoon 400 for nearly three years (sold Dec 13).

We sailed in the Channel both sides, mainly west from IOW, as far as IOScilly.

We dried out whenever we wanted and had no issues with the stability of the boat, any deformation of the structure, or any problems with rudders etc.

However, the Lagoon may just suit this type of use. I know that say the Gemini cat sits on the wider parts of its hull rather than the keels and so one would want to perhaps be more careful. Other brand may be the same. Also, the Lagoon is pretty heavily built but the price of this is that they don't sail too fast either.

The 400 had a high freeboard and was difficult to get off when on hard sand. Even using the stern ladder required a bit of leap from the last step.

We dried out for convenience, and for practical purposes such as checking for prop damage after running over obstacles etc. I also did a couple of hull scrubs between tides which was a knackering job on the 400 because it felt like scrubbing x2 medium sized monohulls.

I have seen pictures of Lagoon cats in the Lagoon yard with support under the bows but we never bothered and it was fine. Since the engines are close to the stern, I think there is plenty of counterweight for anything that may lower the bow. Having said that, we used to slowly run 'up' a beach to get firm so probably always leaned sternwards a bit when dried out on a sloping beach.

For me, a great advantage of being able to dry out is that we could moor in relatively shallow water, where no one else wanted to/could anchor, and if we half dried out at the bottom of tide, it was fine. Standing tall dried out on a beach put some of the service gear like genny, toilets etc out of use for too long so this wasn't often our preferred option.

Garold

 

[SeamanStaines]

Whilst we had our cat (Leopard 42) in the Bristol channel (and the West country) we dried out all over the place including a couple of times accidentally on rocks, never had any issue at all. There was never problem either settling or rising off and compared with a bilge keeler which always seemed to want to dance around and pound the keels through the hull!

 

[tcm]

I reckon quite a few biggish catamarans are owned by folk who sail predominantly in UK waters, for whom drying out is an issue!

Well, okay, a few. But looking out in to the bay here in St Martin HALF of all the boats are catamarans.

Garold's point is very valid - once dried out there's no loos or generator, so that "floating luxury apartment" thing is lost.

So the ability to dry out is a "handy feature" rather than a "massive selling point", I think.

 

[Adonnante]

Well, okay, a few. But looking out in to the bay here in St Martin HALF of all the boats are catamarans.



So how many is a few? Here in Millbrook in Cornwall on the most recent Google Earth pass (08/2009) I've just counted 39 multis afloat and 19 ashore, that's pretty typical, all in a lake of the Tamar.

 

[Greenheart]

Broadening the question slightly, isn't it perfectly possible to fit a holding tank and flushing water supply, so use of the loo isn't restricted when the hulls are high and dry?

Pardon the dumb question, but why is use of the generator not possible, out of the water? Is it a cooling water issue? Couldn't a reservoir be installed for that too?

Granted, no-one selects a boat purely with ability to dry-out as their guide - but reflecting on deep water mooring fees, and the high cost of visitors' berths, and the sheer freedom of choice which you lose if you can't dry out, I'd think the ability to dry out anytime whilst cruising, plus routinely on the home mooring, would make it very appealing...

...perhaps not so if one's cruising grounds aren't tidal, or are littered with excellent unfrequented anchorages...but I'd regard not having the freedom to dry out as a real loss.

 

[RichardS]

Broadening the question slightly, isn't it perfectly possible to fit a holding tank and flushing water supply, so use of the loo isn't restricted when the hulls are high and dry?

Pardon the dumb question, but why is use of the generator not possible, out of the water? Is it a cooling water issue? Couldn't a reservoir be installed for that too?

Granted, no-one selects a boat purely with ability to dry-out as their guide - but reflecting on deep water mooring fees, and the high cost of visitors' berths, and the sheer freedom of choice which you lose if you can't dry out, I'd think the ability to dry out anytime whilst cruising, plus routinely on the home mooring, would make it very appealing...

...perhaps not so if one's cruising grounds aren't tidal, or are littered with excellent unfrequented anchorages...but I'd regard not having the freedom to dry out as a real loss.

In theory the answer to both your questions is yes ..... but.

The loo is either going to have to use fresh water which is usually not in unlimited abundance or sea water, which means another tank somewhere taking up space.

Generator cooling is more problematic than you suggest as you need a continuous supply of cool water or a method of re-circulating the water and cooling it through some kind of radiator / heat exchanger which is more complicated and costly. I don't actually have this problem as I have an air-cooled portable generator so there is a solution but it's not as convenient as an installed genny and they usually water cooled.

Richard

 

[Greenheart]

Thanks, I see. But it still sounds like these would only represent problems if one reached opportunities to dry out without having foreseen what the on-board systems require.

It'd be unfortunate, never to benefit from a cat's ability to sit comfortably upright on any clean bottom, simply because one hadn't equipped basic systems to cope between tides.

I'd regard a catamaran big enough to have standing headroom on the bridgedeck, as a fantastic floating apartment, because if she can park safely in shallow creeks or drying bays that are out of bounds to keelers, that versatility is hard to beat...whereas, if a cat's design wasn't any freer to take the ground than a single keeler, I doubt I'd consider her.

 

[prv]

Thanks, I see. But it still sounds like these would only represent problems if one reached opportunities to dry out without having foreseen what the on-board systems require.

Well, for what it's worth, Steve Dashew's Wind Horse can use all her systems when on the hard. Freshwater flushed heads as they have a huge watermaker (in fact during a typical passage they make more water than they use, as ballast to counteract the fuel consumed), and the generator, fridges and freezers use very large keel coolers which have enough surface area to lose all the heat to the air. But the FPB boats of which she is a prototype are, shall we say, somewhat unusual.

Pete

 

[Greenheart]

Hmm...impressive...although it sounds slightly barmy, or at least far from green, to run water-makers which require generators whose appetite for fuel is so great, some of the water produced is needed as ballast to compensate for the weight of fuel burned!

I expect I misunderstand.

I'll be off the air for a while...I'm off to the land of NoFi. :encouragement:

 

[prv]

it sounds slightly barmy, or at least far from green, to run water-makers which require generators whose appetite for fuel is so great, some of the water produced is needed as ballast to compensate for the weight of fuel burned!

The FPBs are motor boats, though with a design inspired by the sailing boats that Dashew spent most of his career on. So they have an efficient hull shape and use much smaller engines than a traditional mobo of the same length. They don't use generators underway, the main engine alternator(s) supply more than enough power. But Steve and his wife do seem to have a bit of a laundry fetish (they mention running the washing machine every other day) and like anyone they enjoy a good shower, so the boat is equipped to provide almost unlimited fresh water. Since the hull works better with enough weight to cut through the waves rather than bounce over the top, when low on fuel they direct some of this water into the tanks.

The newer versions of the FPB design have a lot of solar panels on top, with the goal of not having to run the generator even at anchor. That goal is achieved as long as you don't insist on running too much air conditioning, and they've paid a lot of attention to ventilation and shade to help you with that.

(Wind Horse, the prototype FPB)

Pete

 

[snowleopard]

First thing to remember is that cats don't have ballast keels to sit on so any fins are likely to be of lightweight construction and not too happy about sitting on a sharp rock. Some have keel shoes of steel or wood fitted for that reason. I have a half-tide mooring on soft mud and only have about 7mm of GRP on the bottom of the keels but that works fine for me.

As regards twisting of the structure when not fully supported, it shouldn't be a strength issue as any boat damaged by lack of even support would break up in any sort of sea! Having said that, cats generally have some flexibility and when mine comes ashore for the winter we have to check the cabin door will open and adjust the packing to suit.

Boats with dagger boards would normally have a stub keel aka grounding shoe on the bottom. Some racers don't and I'd be very wary of those. The most extreme I've seen is a tri with no grounding plate and a prop shaft forming the lowest point - it has to sit on 2 ft thick baulks of timber in the yard.

 

[Birdseye]

I was reading an old cruising thread elsewhere...sorry I don't have a link to it. But it raised the point that lots of people dream about the versatility of quite large catamarans being conveniently beached, and safely left to dry out in beautiful locations which are inaccessible to almost all other yachts...

...and the suggestion was clearly made that some catamaran builders are keen to promote this image of large cats being easily dried-out in idyllic spots, whereas doing so may actually endanger the vessel's structure, not only because of obvious risks like occasional rocks on a sandy beach holing the hull, but because big cats require carefully-judged placing when drying out, as their structural stiffness may be compromised when all the vessel's weight is only supported on three corners.

I'd be interested to read owners' accounts of drying out in catamarans over about 35ft - particularly if these stories demonstrate or disprove the claimed danger.

You dont dry out any boat deliberately without knowing whats underneath, not if you are wise. That said I dried out my cat without checking a number of times, all because the "float on a wet lawn" mentality you get causes carelessness and casualness and running aground. Never a problem but it was a Prout cat and not one of these french things. It also had sacrificial keel shoes.