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Old 18-04-2018, 08:42   #1
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Cost to build

I've been looking at catamaran study plans for two cats. One about 32% longer than the other from the same designer. One is a tad small, and the other significantly larger than I want. What I find interesting is that the with a 32% increase in length, the bill of materials shows almost double the amount of plywood.....
I'm a believer in the adage about buying or building the smallest boat that will do the job, not the largest one that you can afford.
Both are capable voyaging catamarans, plywood construction, and actually quite similar. Simple construction, well designed with the bridge deck beginning well aft, and well streamlined low profile bridge deck cabins. The one lacks standing headroom....... as it should for it's size, in order to have good bridge deck clearance. The other has standing head room for me..... I'm not tall. Head room is not a make or break deal for me. The big headache is the fact that I would have to build at home, and haul the separate hulls to a boatyard to assemble and finish the boat. It would be nice to be on a waterway that connects to an ocean, but that just isn't going to happen.

H.W.
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Old 18-04-2018, 10:28   #2
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Re: Cost to build

Consider the proceeds a 30 ft cat vs a 40 ft (33% longer) cat from the same builder. Wouldn't surprise me that materials and cost would be double.
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Old 18-04-2018, 10:37   #3
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Usually the Study Plans give a breakdown of materials and estimated build time in hours/week worked.. at least James Wharram plans do..
That info should get you prices on the end of a phone.
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Old 18-04-2018, 14:37   #4
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Re: Cost to build

32% increase in length implies a similar increase in other dimensions for a similar design.

So you are looking at something like 1.32 x 1.32 = 1.74 or 74% increase in surface areas.

(And you are looking at 1.32*1.32*1.32 = 2.29 (more than double in volumes)

And of course, corresponding increase in weight and rigging loads etc so all of your fittings need to be stronger/heavier/more expensive
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Old 18-04-2018, 18:41   #5
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Re: Cost to build

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Originally Posted by StuM View Post
32% increase in length implies a similar increase in other dimensions for a similar design.

So you are looking at something like 1.32 x 1.32 = 1.74 or 74% increase in surface areas.

(And you are looking at 1.32*1.32*1.32 = 2.29 (more than double in volumes)

And of course, corresponding increase in weight and rigging loads etc so all of your fittings need to be stronger/heavier/more expensive
That's pretty much the way my math goes......... Which is why I'm trying to adhere to the adage about the smallest boat that will do the job..... Expenses don't end with plywood, they don't end with rigging and sails....they don't end until the boat is resting on the bottom, and maybe not even then ;-)

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Old 20-04-2018, 01:18   #6
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Re: Cost to build

Some years ago I did fairly detailed costing for Richard Woods' Gypsy (8.5m) and Romany (10.5m) cats. Excellent home-build designs with a proven record of safety and good sailing performance, many ocean miles, full headroom throughout.

Romany is basically a Gypsy with bigger hulls.
I don't have the exact figures to hand, but the bigger boat cost nearly double, around $70k+ vs $35-40k,despite being only 2 metres longer.

Also a lot more surface to clean, antifoul, paint. Repairs and replacements over time will all cost more. It will take more muscle to get the main up.

"The smallest boat that will do the job..." Whoever said that knew what he was talking about.
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Old 20-04-2018, 03:23   #7
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Re: Cost to build

However, if you just make the hulls longer, it really doesn't cost much more at all.....
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Old 20-04-2018, 03:38   #8
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Re: Cost to build

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Originally Posted by Teleman View Post
Some years ago I did fairly detailed costing for Richard Woods' Gypsy (8.5m) and Romany (10.5m) cats. Excellent home-build designs with a proven record of safety and good sailing performance, many ocean miles, full headroom throughout.

Romany is basically a Gypsy with bigger hulls.
I don't have the exact figures to hand, but the bigger boat cost nearly double, around $70k+ vs $35-40k,despite being only 2 metres longer.

Also a lot more surface to clean, antifoul, paint. Repairs and replacements over time will all cost more. It will take more muscle to get the main up.

"The smallest boat that will do the job..." Whoever said that knew what he was talking about.
That is one way of looking at it. Another is that longer is faster, with a better motion, and as anyone who has been in a bad storm will attest, bigger feels (and is) safer.

The trick is to go longer without going higher or wider. The best way to do this is a proa, where only one hull needs extending. The 15m/50' harryproa at in cruising trim weighs 3.5 tons vs the 11.5m/38' Romany at 4 tons. A 40'ter weighs 800kgs, half as much as Gypsy

If you want to minimise maintenance (and build time, hard work and exposure to toxic material), then plywood is a poor choice. Much better is Intelligent Infusion, where the atmosphere does all the laminating and there is no post infusion grinding or cutting of cured laminates and nothing to rot.
see INTELLIGENT INFUSION – Harryproa.

Stayed rigs are also a poor choice for minimising maintenance. And for reducing the fear factor. Unstayed rigs are step and forget and allow you to raise, lower, reef and completely depower the entire rig on any point of sailing. No flogging sails and no foredeck work.

As for cost, the materials for a ply, frames and stringers cat cost a little less than the same weight of foam and glass. But given the weight difference, the reduction in waste and the lower tool requirement, the infused proa is way cheaper.

I'm happy to expand on any of this that is not clear, either here or email me at harryproa@gmail.com
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Old 20-04-2018, 06:00   #9
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Re: Cost to build

I wanted to build a 10 meter cat, but the extra costs of berthing and slipping just did not ad up. In the end we built a 10 meter swing keel plywood monohull that cost $30,000 AUS in materials in 2016. The cost from home to the marina was only $500 on the back of a tilt tray truck.
If you build your cat keep a daily eye on the internet for cheap sailing gear. I picked up lots of stuff that way.
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Old 20-04-2018, 08:42   #10
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Re: Cost to build

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Originally Posted by Teleman View Post
Some years ago I did fairly detailed costing for Richard Woods' Gypsy (8.5m) and Romany (10.5m) cats. Excellent home-build designs with a proven record of safety and good sailing performance, many ocean miles, full headroom throughout.

Romany is basically a Gypsy with bigger hulls.
I don't have the exact figures to hand, but the bigger boat cost nearly double, around $70k+ vs $35-40k,despite being only 2 metres longer.

Also a lot more surface to clean, antifoul, paint. Repairs and replacements over time will all cost more. It will take more muscle to get the main up.

"The smallest boat that will do the job..." Whoever said that knew what he was talking about.

The woods Gypsy and Romany didn't make the cut for several reasons, though the Sagitta comes in close to what I want. The Gypsy and Romany do not have hulls that connect to the bridge deck cabin, and that's a big deal, as I intend to live aboard more or less permanently, as a live aboard voyager. I want the spaces conveniently connected. Both boats also have nacelles hanging down from the bridge deck cabin, which while it is a logical compromise, just does not give me that "warm and fuzzy feeling". I will say that Richard did a good job with the nacelles, keeping them fairly small, with a sharp bow, and well aft, so they probably do not present a pounding issue. The third factor, is payload. I went away from trimarans due to payload per length. The 1200 lb payload of the Gypsy just doesn't cut it. The Romany with it's 3000 lb payload makes the cut in that respect. It's a lot more boat. On the other hand Sagitta comes very close to the mark. It stays within the 30' window, and still offers 2000 pounds of payload. My ideal cat would be Sagitta with Bernd Kohler's trapezoidal hull design, which would both bump the displacement up, and simplify construction. I need a load carrying voyaging boat, not a performance boat. The full more or less panoramic visibility in Sagitta, and the interior layout with hulls and bridge deck joined, make it pretty ideal. It means that in dirty weather, one can mostly keep watch from inside. I don't need standing headroom on the bridge deck, and with companionway sliders open, in nice weather, there is only a fairly small non-standing area. The bridge deck is mainly a sit down lounge area, and will be my sleeping area, as I've slept in a recliner for many years anyway.

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Old 20-04-2018, 09:19   #11
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Re: Cost to build

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Originally Posted by rob denney View Post
That is one way of looking at it. Another is that longer is faster, with a better motion, and as anyone who has been in a bad storm will attest, bigger feels (and is) safer.

The trick is to go longer without going higher or wider. The best way to do this is a proa, where only one hull needs extending. The 15m/50' harryproa at in cruising trim weighs 3.5 tons vs the 11.5m/38' Romany at 4 tons. A 40'ter weighs 800kgs, half as much as Gypsy

If you want to minimise maintenance (and build time, hard work and exposure to toxic material), then plywood is a poor choice. Much better is Intelligent Infusion, where the atmosphere does all the laminating and there is no post infusion grinding or cutting of cured laminates and nothing to rot.
see INTELLIGENT INFUSION – Harryproa.

Stayed rigs are also a poor choice for minimising maintenance. And for reducing the fear factor. Unstayed rigs are step and forget and allow you to raise, lower, reef and completely depower the entire rig on any point of sailing. No flogging sails and no foredeck work.

As for cost, the materials for a ply, frames and stringers cat cost a little less than the same weight of foam and glass. But given the weight difference, the reduction in waste and the lower tool requirement, the infused proa is way cheaper.

I'm happy to expand on any of this that is not clear, either here or email me at harryproa@gmail.com
Harry:
While plywood epoxy is perhaps not the fastest, and least labor, it is extremely efficient in terms of strength to weight ratio, and a well proven construction method. Foam core requires glass inside and out to achieve any strength, and I'm not convinced that structural core and load bearing surface plies work together satisfactorily. Foam core has progressed from one unsatisfactory core to the next to the next in boat building, each one being the ultimate. Marine plywood properly sealed has a very long track record and is well proven, with properly home built plywood epoxy boats 30+ years old still sound. The only real fly in the soup is individual construction variations, as most are home built. Foam has the advantage of not being subject to rot. It also offers sound deadening, and insulation, all are big positives. You will never convince me that a proa is the right choice, even some of the most die hard proa guys have moved on to other planforms, and for good reason IMHO.

I am however totally in favor of the free standing mast. The weight may be greater.... though not a lot greater due to the weight of standing rigging, spreaders, etc, but the reliability is immensely superior. All your structural strength is in the mast itself, and you do not rely on dozens of fittings, swages, cables, etc, any of which can bring the entire works down if it fails. That makes great sense to me, though there are die hards that just can't seem to see that.......... If any component of the backstay fails, the mast is likely going down, nothing else offers any redundancy, the same is true for the shrouds and forestay, and of course all those chain plates are points to fail and to leak...... a nighmare IMHO, but one we have all come to accept as "normal".

Interestingly in the Queen's Birthday storm, most of the monohulls were dismasted, but none of the multihulls. The Simpson Catamaran Ramtha was abandoned, but later recovered completely intact, as was Richard Woods Eclipse more recently off Central America. Multihulls are incredibly seaworthy, the human element seems to be the weak point.

H.W.

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Old 20-04-2018, 19:43   #12
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Re: Cost to build

Owly, wouldn’t the beam strength required to step a freestanding mast between the hulls eat a big chunk of payload ?
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Old 21-04-2018, 04:28   #13
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Re: Cost to build

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Harry:

While plywood epoxy is perhaps not the fastest, and least labor, it is extremely efficient in terms of strength to weight ratio,
No it isn't. A frame and stringer ply boat will be about 20% heavier than an infused foam/glass one for the same strength and stiffness. Let me know the specs of the ply boat and i will do a weight comparison showing this. The ply boat will take about twice as long to build and most of the labour is either hard, sticky or dusty.

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and a well proven construction method. Foam core requires glass inside and out to achieve any strength, and I'm not convinced that structural core and load bearing surface plies work together satisfactorily. Foam core has progressed from one unsatisfactory core to the next to the next in boat building, each one being the ultimate. Marine plywood properly sealed has a very long track record and is well proven, with properly home built plywood epoxy boats 30+ years old still sound.
there are plenty of ply/epoxy boats older than that. The oldest foam glass multi is one of the early Kelsall ones (Trifle, I think), built with polyester resin in 1966 (52 years old) and still going strong. Great Britain 2 (mono) was built in 1972, also polyester/foam glass. Raced seven times round the world, 50 plus Atlantic crossings and a very busy sailing career in between.

Foams, resins and build techniques have improved a lot since then, plywood quality has arguably gotten worse.

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The only real fly in the soup is individual construction variations, as most are home built. Foam has the advantage of not being subject to rot. It also offers sound deadening, and insulation, all are big positives.


Indeed. That makes it about 7-0 in favour of foam/glass. I have been in the boat business for 45 years, built dozens of boats, helped hundreds of builders with ply, strip, double diagonal and hand laid glass/foam with and without vacuum. None come close to the labour saving and weight gains possible with Intelligent Infusion. Maybe try an infusion before you start and weigh, bend, break and abuse the result in any way you can think of. Then do the same with ply. At least then, you will have the knowledge to make the comparison.

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You will never convince me that a proa is the right choice, even some of the most die hard proa guys have moved on to other planforms, and for good reason IMHO.
You are talking about Pacific proas or proas based on traditional types. None of the large harryproa owners have sold their boats. The 'good reasons' for not cruising on a Pacific proa have all been designed out of harryproas. If you could list the reasons why "you will never be convinced", maybe i can point out how or if they have been addressed.

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Multihulls are incredibly seaworthy, the human element seems to be the weak point.
I could not agree more. The less stress there is on the crew, the more likely they are to survive a storm. Examples of stress reduction on harryproas:
Tacking and gybing in high winds/big seas are not a problem as you shunt and can sail in either direction.
The sea anchor can be deployed over the stern as the boat is double ended.
The sterns are well aft of the deck, so less chance of being pooped.
Small, well drained cockpit and no dinghy hanging in davits.
The cabin doors are to lee of the windward hull, not behind it, so pooping will not flood the cabin or imperil the doors.
For a given weight, they are much longer and wider, so far less likely to suffer a wave capsize, or to heel and pitch as much.
Rudders (no boards) can be lifted clear of the water, further reducing the odds of a wave capsize and along with the reduced draft from rockerless hulls, seriously reducing the strain on the sea anchor cable.
The bunks are central, so movement is less.
Simpler, so less to go wrong, and as importantly from a stress point of view, less to worry about..
No flogging sheets (or wind screaming in the rigging) to scare the crew.
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Old 21-04-2018, 06:17   #14
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Re: Cost to build

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Owly, wouldn’t the beam strength required to step a freestanding mast between the hulls eat a big chunk of payload ?
Actually a free standing mast requires far less "beam strength" than a stayed mast. The beam must carry longitudinal and lateral loads, but almost no vertical loading.... only the weight of the mast, sails, etc. On a stayed mast, the stays are trying to drive the mast through the bottom of the boat due to the tension. The loading is completely different. What is required is bury, and lateral and longitudinal loading bearing both at the step, and at the partner where the mast emerges from the cabin top.

Take the Woods Sagitta, one of the designs that fits most of my criteria, the existing mast beam is in excess of the needed strength vertically, and laterally, and as it ties into the bridge deck, it also is plenty strong longitudinally. Where the problem comes in is where the mast emerges from the coach roof. This area, known as the partner, must support and transmit the lateral and longitudinal loads to the rest of the structure. It in effect takes the loads that the stays and shrouds would. Those loads will be multiplied by the difference in the lever arm, but divided by the angular inefficiency of the shrouds. The coseacant of the angle is the factor one multiplies the actual load on the mast by to determine the load on the shrouds or stays.
In any case, the coach roof must have sufficient reinforcing built in to carry these loads out to the hulls, but that's not a huge challenge, and with carbon fiber, it could be done without a great deal of additional weight.

H.W.
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Old 21-04-2018, 08:40   #15
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Re: Cost to build

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Actually a free standing mast requires far less "beam strength" than a stayed mast. The beam must carry longitudinal and lateral loads, but almost no vertical loading.... only the weight of the mast, sails, etc. On a stayed mast, the stays are trying to drive the mast through the bottom of the boat due to the tension. The loading is completely different. What is required is bury, and lateral and longitudinal loading bearing both at the step, and at the partner where the mast emerges from the cabin top.
You forgot the bending stress with an unstayed mast. For the most part the forces are different not greater or lessor.
- With a stayed mast, the mast exerts a significant downward force in the center and the stays add an upward force on the sides. This creates a bending force in the beam.
- With an unstayed mast, the mast step needs to resist that bending force at the point it sits on the deck...or more realistically, you have an upper and lower support point. With a monohull, that can be at the keel and the deck with 8-10' separation allowing it to resist the bending force. With a cat, it's often had to get more than 4-6' f separation (assuming modest size boats)
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