Beaching small multihulls for service

[Seabeau]

Originally Posted by catsketcher

I like John Marple's idea that multihulls are great boats is because they can be very shoal draft whilst not reducing seaworthiness or interior amenity.
A cat, as opposed to a trimaran and far more than a shoal draft mono, has a large resistance to wave generated capsize because of its far greater roll moment of inertia. Roll moment of inertia is determined by how spread apart large masses are. Increasing roll moment increases the resistance of an object to rolling over in beam on waves.

As such, a shoal draft mono of similar length would almost always have a lower roll moment of inertia than a cat. So a cat resists waves breaking abeam better than monos. Add on the extra stability at low heel angles (compared to monos) and the maths says cats and monos have far different characterstics in large waves.

Richard Woods is the guy to come in here. He did tank tests in the Southampton wave tank with cat models. Whilst tank testing cat models, he found it impossible to get cat models to capsize whereas the mono models could be capsized.

https://www.sailingcatamarans.com/in...ability-part-3

Thanks for the article. Great stuff from back in the day.

Richard Wood's information curve is based on wind generated loads and not breaking waves.

[Seabeau]

Originally Posted by Tupaia

True and I agree, but you have to consider the stability curves for the two different types.

Which two different types? Catamarans and Trimarans? Of mono's and multi's? With initial stability, the salient issue is, that the least resistant hull, in relation to sideways motion, is the least affected by breaking waves. Breaking waves, where the wave top is moving at greater speed in relation to the lower parts of the wave. Ultimate stability is another issue, and only comes into play, after the results of the failure of initial stability.

[catsketcher]

Originally Posted by Seabeau

Which two different types? Catamarans and Trimarans? Of mono's and multi's? With initial stability, the salient issue is, that the least resistant hull, in relation to sideways motion, is the least affected by breaking waves. Breaking waves, where the wave top is moving at greater speed in relation to the lower parts of the wave. Ultimate stability is another issue, and only comes into play, after the results of the failure of initial stability.

Gday Seabeau

A lot of work on capsize resistance was completed in the 80s. Back then people wondered why cats and tris were so different in beam seas. Cruising cats started getting better, and people started wondering why cats were so resistant to wave induced capsize whereas tris were very prone.

Stability curves were not the only important factor, neither was the ability to slide sideways. A good tri with high volume floats will slide sideways well. A Piver has inward sloping amas that are high volume. What was found was that it was the very fact that cats had two large masses at their extreme beam. This imparted a large amount of rotational inertia to the cruising cat - a factor not shown by stability curves.

Basically, we learnt back in the 80s that a tri and cat with the same amount of stability (the area under the stability curve) were affected very differently by breaking waves - and not by sliding down the waves. Just by the ability to be rotated by the crest. The cat was far more resistant to rotation in the time the crest moved by it, than the tri (which has a much lower roll moment).

There are lots of dynamics involved in capsize. The Wolfson institute went through many aspects of this and beam seas can be a worry for all boats. Multis have some issues with short waves as the boats become effectively very light when falling off a wave. This can lead to wind and wave induced capsize as stability is reduced by the reduction in weight. This is something all dinghy sailors can feel when sailing in big waves, you gotta ease the sheet big time when you fall off the wave or you go over.

I have not sailed my cat in large breaking swells. I don't think I ever would be sailing beam on in large breaking swells at any time. The accelerations would be too high and it would be too dangerous. Way before that time I should be sailing slowly to windward with my staysail and reefed main, downwind with my drogue out, or lying to the parachute. Monos may be happy forereaching or heaving to, and beam on, but this possible mono technique is not something any of my cat friends talk about - its is drogues and parachutes but never beam on.

As the techniques used in large waves are different it doesn't make sense to use the same metric to compare monos and multis. Even tris need different techniques from cats.

[owly]

Stability and capsize resistance, monohull versus catamaran has been hashed over many times. Invariably numbers are thrown around relating to "stability" that are NOT valid to be applied to both types. Voyaging / cruising cats are sailed over, not flipped by waves, and that is a matter of poor seamanship / poor judgment. They will not right themselves, and that strikes unreasonable fear into the hearts of some sailors, but it's not an issue unless you turn one over.....The waves of a storm are not going to do it as a rule. We have had many years of examples to confirm this. Cats abandoned in vicious storms with the sails down carry on and stay right side up.

On the other hand monohulls routinely get knocked down, and sometimes capsized in storm conditions. There are countless accounts. It may give you comfort that your boat should turn back right side up.......... but the story repeats with monotonous regularity..... Weighted down by the water it took during the capsize, or even knockdown, the sailor finds he is swept by waves more often. He also finds that his bilge pumps do not work because of all the crap that has floated into them, having to resort to buckets, ultimately failing to keep up and abandoning ship. The French company ETAP is the only manufacturer of unsinkable sailboats I know of. Your boat is likely going down once capsized........The old saying is that you should step UP into your life raft........ presumably in hopes that you can recover the boat.... or is it with the idea of making sure you have enough stuff aboard?

My biggest concern in storm tactics is preventing rudder damage, either on a multi or a mono. It is a common issue that has resulted in abandonment of both multihulls and monohulls. A weak point you cannot address in storm conditions as a rule. I believe both Rainmaker and Ramtha had rudder issues when they were abandoned...... both "recovered" right side up.



Reading about capsize of trimarans versus catamarans I am reminded of playing on a piano stool as a child.......Discovering that sticking my legs out, I decelerated my spin, and pulling them in I accelerated....... Think of two heavy hulls outboard versus two light weight amas... it's pretty easy to see that it takes a LOT more energy to accelerate the one heavy hull about the axis of the other than to accelerate the light weight ama about the central hull. You may have flotation out there, but not inertia.

[owly]

Some Crazy Thoughts ;-)


This thread has drifted far from what I had intended, and I'd like to thank those who have given me some real insights of value on beaching, and some practical considerations. It is clear that the type of bottom is important...... but that was already obvious.... If one plans to work on a mud bottom, something to stand on other than the actual mud is going to make all the difference. It also makes sense to put something under the keels on any bottom. Needless to say a place like the Bay of Fundy or northern end of the Sea or Cortez, or NW Australia, and a number of similarly high tidal range areas are desirable. It is also clear that planning to do bottom paint is perhaps unrealistic, depending on tidal range, weather, and the paint itself...... Clearly a multi tide multi day undertaking..... prep on one day(or several), wipe and allow to dry in the sun, use a fast drying paint, and keep areas small enough. Not a simple easy process that anybody can do with any paint in any weather. Real serious planning.
It was brought up that I'm "poor" (as I myself said), when copper bottom paint was suggested. "Poor" is relative. My question would be cost over time. Does the copper last enough longer for a break even? If I could scratch together enough for a copper bottom during a haul out, where does that leave me? If it eliminates enough haul outs and yard fees, it could perhaps be cheaper in the long run. Being "poor" doesn't mean that I cannot spend money when it saves me money to do it. Does that makes sense?

It is also true as someone pointed out that there may be little bottom work I can do on the beach....... little to do. I would never choose inboard diesels over outboards on a catamaran. Weight, up front cost, ability to pull the engine up out of the water for service easily, elimination of prop drag, elimination of ALL through hulls below the waterline related to the engine, elimination of stink and noise of the diesel in the hulls Inboard diesels are for motorsailors IMHO. I'm very mechanical, and have rebuilt (real full rebuild) literally hundreds of engines, many of them diesels, currently working on an Isuzu 2800. I want engines I can get to easily, not bathed in salt water all the time. My ideal boat would have zero through hulls below WL.... unless you count the depth sounder.
Swimming to scrape the bottom makes some sense. Less sense if you are single handing, at least at sea. A hooka rig might be a good investment, and the ideal location would be one with a light current to carry stuff away so you can see.

An interesting thought that nobody has ever brought up that I recall seeing is using a watermaker pump to drive a pressure washer. The pumps are basically identical / interchangeable. As a "poor man", I consider a watermaker non-negotiable, but must be home built. It means I can get by with a smaller payload of water / smaller cat, which will cost less all the way down the line. It also means that I do not have to depend on questionable water in remote parts of the world, or buy water where water is scarce. The technology is dirt simple, and parts are readily available. There are problems for me. One is scale..... I would want a very small capacity unit so I could run it virtually every day....... they live longer that way. Ideally it would be driven by solar power........... Fresh water and refrigeration (stored cold) are "batteries" as far as I'm concerned......... I'd rather store coldness than electrons.... Ice doesn't wear out. If you are making water anyway, it just makes sense to use it as a form of energy storage when the sun shines rather than storing in a battery to mindlessly use as if one were connected to the grid. I've lived off grid before so these kinds of things naturally come to mind. The scale for making water in small quantity and the power source do not lend themselves well for pressure washing. An elegant solution if it could be made to work both for hull cleaning and washing down the rest of the boat, ground tackle, etc. Just a wild thought, and I have no real solution to make it work well for both on a small boat scale unfortunately. My current washer (cold) runs 3000 psi at 12 GPM, and works the hell out of a 25 HP engine....... it would clean a boat very quickly with the rotary nozzle that will cut a 2x6 in half in about 20 seconds, splinters flying...... a bit more than needed ;-)

[catsketcher]

You don't need the pressure cleaner Owly. Just put the boat in about a metre of water and gently go around and rub her bum - with a scourer or some wet and dry paper. I have done this for over 20 years and don't even get my hair wet. It is easier than doing it on the dry because my arm floats a bit. I know my boat and can reach all her bum with an outstretched arm. If she was much bigger than 38ft this would become difficult. You will need to do this if you use Coppercoat, at least all my friends who have it scrub regularly.

I would be fine to do the antifoul in between tides in certain areas - large tides, no one around and some timber pallets cut in half to pop her on. In summer the paint would be dry in time for the tide to come back in. If you do it somewhere like Island Head creek (On the Queensland coast) where there is a 5 metre tidal range - you may not even get wet on the second high of the day. Re-adjust the pallents and float again on a second day. I would seriously consider this if I was a little short of cash.

As for through hulls - our outboard powered cat has three, one for the log (don't bother - I haven't used it in decades), one for the toilet and one for the salt water inlet (on the other hull) - the depth sounder is epoxied in and very strong so I don't think it qualifies as a through hull anymore. I like only having a few through hulls, even our holding tank empties above the waterline (just) and the deck wash uses an inlet pipe thrown in the water. We only open the holding tank seacock underway and well out to sea so you can't really tell there is a trail of waste unless you look.

[Mr B]

I beach my cat in a metre of tide, I pick a nice sandy beach to park my cat on,

I have used a pressure washer to clean my hulls using my fresh water tanks,
It was a total waste of time and fresh water,

Its a 240 volt pressure washer, I also use it to run my water maker, It runs off my 3000 watt invertor from the batterys,



When I am on a beach, My water inlet for the motor is sitting on the beach under the boat, So no using my Diesel,



I use a long handled scraper, its 6 inches wide, It takes all the molluscs off the boat very easily,

It came out of the ocean and its going back into the ocean,

So its not pollution,



It takes me 3 hours to scrape my hulls on a dry sandy beach,

North side of Phillip Island, Victoria, Australia,

I dont get wet, Even tho I am kneeling under the boat,

I also pick my days when there is no wind or waves,
It helps when you have a 600 mm or two foot draught,



Only beach on a 3/4 tide height, You might have to wait a few days or a month if you go in on a full high tide,

[owly]

Originally Posted by Mr B

I beach my cat in a metre of tide, I pick a nice sandy beach to park my cat on,

I have used a pressure washer to clean my hulls using my fresh water tanks,
It was a total waste of time and fresh water,

Its a 240 volt pressure washer, I also use it to run my water maker, It runs off my 3000 watt invertor from the batterys,



When I am on a beach, My water inlet for the motor is sitting on the beach under the boat, So no using my Diesel,



I use a long handled scraper, its 6 inches wide, It takes all the molluscs off the boat very easily,

It came out of the ocean and its going back into the ocean,

So its not pollution,



It takes me 3 hours to scrape my hulls on a dry sandy beach,

North side of Phillip Island, Victoria, Australia,

I dont get wet, Even tho I am kneeling under the boat,

I also pick my days when there is no wind or waves,
It helps when you have a 600 mm or two foot draught,



Only beach on a 3/4 tide height, You might have to wait a few days or a month if you go in on a full high tide,

It should be fairly obvious by now that I have not undertaken this job myself. With tidal range running less than 1M in the Melbourne area, it would not seem like there would be a lot of margin....... unlike in Northern AU where the tidal range is almost absurd at around 5M in places. It is not difficult to find tidal ranges in excess of 1M on the US Left Coast, and a lot of other places.



It should be obvious to me...... and anybody else that hard growth is best scraped off, that a pressure washer really would be best suited for the softer growth...... if it makes sense at all ;-( Also that running one on battery through a 3K inverter is going to limit it's size, usefulness, and run time. Probably better for general clean up.

I find it interesting that you used fresh water when your watermaker pump / pressure washer is designed for salt water. I would presume your washer motor was pulling about 1200 - 1300 watts, about the same as most home owner electric pressure washers (1.5 HP). That would make it marginal at best for the job, and you would eat battery capacity pretty rapidly.

I was just speculating about the possibility of utilizing a watermaker pump as a pressure washer (or vice versa). It could be useful for cleaning above the WL and topside as well as ground tackle perhaps, though low pressure and more volume would probably be more effective for the latter job. In any case, as I suggested, I would want a very small watermaker so it could be run daily, which is better for longevity of the membranes by all reports. I would have no hesitation about building one rather than buying one...... I've talked about ideas on that before. Commercially they are built for convenience rather than energy efficiency...... but that's another topic.

[alamoana]

Originally Posted by chalkgsy

Anyone know if you can beach pretty much any Cat then? I have this old video of a privilege 37 I'm buying and was wondering if that kind of hull looks normal and is ok for parking on sand etc?

Yes, you can beach that P37. Just center your weight and have a piece of wood you can attach to avoid it nose diving in case there is too much weight forward. I would dive the area to avoid sharp rocks or use a wooden plank for the keels to sit on. Good luck

[owly]

Originally Posted by catsketcher

You don't need the pressure cleaner Owly. Just put the boat in about a metre of water and gently go around and rub her bum - with a scourer or some wet and dry paper. I have done this for over 20 years and don't even get my hair wet. It is easier than doing it on the dry because my arm floats a bit. I know my boat and can reach all her bum with an outstretched arm. If she was much bigger than 38ft this would become difficult. You will need to do this if you use Coppercoat, at least all my friends who have it scrub regularly.

I would be fine to do the antifoul in between tides in certain areas - large tides, no one around and some timber pallets cut in half to pop her on. In summer the paint would be dry in time for the tide to come back in. If you do it somewhere like Island Head creek (On the Queensland coast) where there is a 5 metre tidal range - you may not even get wet on the second high of the day. Re-adjust the pallents and float again on a second day. I would seriously consider this if I was a little short of cash.

As for through hulls - our outboard powered cat has three, one for the log (don't bother - I haven't used it in decades), one for the toilet and one for the salt water inlet (on the other hull) - the depth sounder is epoxied in and very strong so I don't think it qualifies as a through hull anymore. I like only having a few through hulls, even our holding tank empties above the waterline (just) and the deck wash uses an inlet pipe thrown in the water. We only open the holding tank seacock underway and well out to sea so you can't really tell there is a trail of waste unless you look.

I have what is probably an unreasonable dislike of through hulls. The head is not an issue as I would consider a composting head the increasingly obvious choice these days. Inshore and offshore are two different situations...... Jim Brown speaks of "bucket and chuck it", and better yet the Spronk head...... just a hole in the bridge deck. Pretty ideal on passage, especially considering that the majority of MOB situations come from pissing over the side or wherever. People act as if human waste is a huge problem in the ocean........ and it is if cities discharge millions of gallons into the ocean......... But sailboats offshore are a non issue in an ocean filled with whale and dolphin poop, not to mention fish waste, etc. Plastics are the problem, not poop.

The salt water inlet through hull below WL cannot be avoided easily or conveniently.........But we are down to one at this point, and making it rugged, and easily accessible for service, it shouldn't be a problem. Growth in through hulls, along with corrosion of materials, leakage of water into the hull material... plywood for example........ Anything submerged in salt water is going to be a problem. Considering a watermaker of some sort this through hull is pretty much a given unless one gets really clever........ or resorts to cave man techniques (buckets).

These are all issues that will be resolved in one way or another over time, and the solutions will differ depending on the individual

[macieknan]

Originally Posted by chalkgsy

... luckily the broker confirmed that you can dry out fine with that model!

I just saw the fins and rudders and thought 'how the hell is that gonna work' but I guess It does...

While most people are great and decent human beings, i would caution against taking brokers word for it. Best to confirm with the designer, builder or other owners, like you are doing right here....

[Mr B]

Originally Posted by owly

It should be fairly obvious by now that I have not undertaken this job myself. With tidal range running less than 1M in the Melbourne area, it would not seem like there would be a lot of margin....... unlike in Northern AU where the tidal range is almost absurd at around 5M in places. It is not difficult to find tidal ranges in excess of 1M on the US Left Coast, and a lot of other places.



It should be obvious to me...... and anybody else that hard growth is best scraped off, that a pressure washer really would be best suited for the softer growth...... if it makes sense at all ;-( Also that running one on battery through a 3K inverter is going to limit it's size, usefulness, and run time. Probably better for general clean up.

I find it interesting that you used fresh water when your watermaker pump / pressure washer is designed for salt water. I would presume your washer motor was pulling about 1200 - 1300 watts, about the same as most home owner electric pressure washers (1.5 HP). That would make it marginal at best for the job, and you would eat battery capacity pretty rapidly.

I was just speculating about the possibility of utilizing a watermaker pump as a pressure washer (or vice versa). It could be useful for cleaning above the WL and topside as well as ground tackle perhaps, though low pressure and more volume would probably be more effective for the latter job. In any case, as I suggested, I would want a very small watermaker so it could be run daily, which is better for longevity of the membranes by all reports. I would have no hesitation about building one rather than buying one...... I've talked about ideas on that before. Commercially they are built for convenience rather than energy efficiency...... but that's another topic.

My thru hulls are sitting on sand, So there is no running the diesel or using my watermaker intake when Im beached,


So I used the fresh water tanks for the pressure washer,

Easily refilled when I get back to the Marina,


North side of Phillip Island has more than enough depth to beach my Cat,
It has a very long clear sandy beach to park on,

I have a draught of 600 mm, with centre board and rudders up,

My drive leg also is raised hydraulically, so its well clear as well,



The Crud, Mollusces and Growth came out of the ocean, I am just scraping them off and returning them to the ocean from where they came from,

It is not pollution in any way,



My pressure washer is a small Karcher, Which I adapted to connect to my Little wonder, water maker, Pressure gauge restricts it to 900 PSI,

It works, Thats all I care about,



I only use it when the diesel is running and Im not parked on a beach,

$100-00 Karcher versus $1200-00 for a little wonder pressure pump motor,

It cost about $60-00 for the stainless steel fittings plus a shorter stainless steel pressure hose, All with quick fit connectors,

[NevilleCat]

Skimming through the thread it seems that your concerns are addressed; yes it is more than feasible to beach smaller cats for maintenance of the bottom and since you are not interested in inboards then maintenance of the outboard mechanics can certainly be done either from your tender or by reversing into the beach.
You don't need much tide to scrub the bottom from the beach...with a long handled mop you regularly wipe of the soft growth before the hard growth can establish itself. Just nose it into the beach on a rising tide if you're in a hurry and you don't need to dry it out for that job. If the beach is steep then do half and spin the boat around by hand with your lines and do the other half. I used to do it all the time at St Kilda beach Melbourne. In winter I had some fishing waders. My boat had boards and drew about 600mm.