Cost to build

[Teleman]

Originally Posted by rob denney

Depends what you call "really useful". The weight difference is 526 kgs/1,157 lbs/just over half a ton, using the numbers below. The empty weight of the boat is 1,800 kgs/3,960 lbs, so the saving is 29%.

The materials list for Woods' 8.8m Saturn specifies (ex waste)
10 sheets 6mm gaboon ply @ 9 kgs per sheet =90 kgs for 30 sq m
52 sheets 9mm gaboon ply @ 13 kgs per sheet =676 kgs for 156 sq m

The exterior of the 9mm is sheathed with 300 gsm cloth and 600 gsm resin (includes filler coat and bog) = 156 sq m x 0.9kgs = 140 kgs.
The interior of the 9 and both sides of the 6mm will/should get 3 coats of epoxy at 8 sq m/litre /coat (Gougeons) = (156 + 630 + 30) x .4 = 86 kgs
Total = 992 kgs

If we leave the stringers in and size the foam/glass for the same stiffness as the ply, we have
30 sq m of 6mm foam with 200 glass each side 30 x (0.5+.2+.2+.2+.4) = 45 kgs
and 156 sq m of 10mm foam with 600 gsm glass outside and 400 inside =156 x (.8+.4+.6+.5+.4)= 421 kgs.
The numbers in brackets are the weights per sq m of the foam+ inside glass+outside glass+infused resin at 1:2 resin fibre+resin to wet the foam both sides.
Total = 466 kgs

Rob, the Woods Saturn uses 25 sheets of 9mm, not 52.
A difference of 351 kilos.
Thus ply hulls 992 - 351 = 641 kilos.

If your foam weights are right, the difference is 175 kilos. As a fraction of the total boat weight, not very significant unless you have racing in mind.

The foam v ply thing seems to boil down to cost and the builder's mindset.
I wouldn't want to have a laminating table out in my garden under a plastic tunnel, but many good ply boats have been built like that. It just takes longer.

A step up in budget and you have a proper shed, another step and you have the plumbing and extra consumables for vacuum bagging or infusion.

The cheapest boat will be a bit heavier and a bit slower, but the view is just as good when you're out there......

[double u]

I'd like to comment on LoA:
serious voyaging for a couple: 40' minimum (payload!)
<33': not for the uninitiated neither for the faint-of-heart nor the "non-spartans"
<30': potential deathtrap
(I know that very capable & tough navigators have made it "around" on 22' cats - everybody is well advised though NOT to consider themselves at par with such exceptionally tough & able people)

[rob denney]

Originally Posted by Teleman

Rob, the Woods Saturn uses 25 sheets of 9mm, not 52.
A difference of 351 kilos.
Thus ply hulls 992 - 351 = 641 kilos.

If your foam weights are right, the difference is 175 kilos. As a fraction of the total boat weight, not very significant unless you have racing in mind.

The foam v ply thing seems to boil down to cost and the builder's mindset.
I wouldn't want to have a laminating table out in my garden under a plastic tunnel, but many good ply boats have been built like that. It just takes longer.

A step up in budget and you have a proper shed, another step and you have the plumbing and extra consumables for vacuum bagging or infusion.

The cheapest boat will be a bit heavier and a bit slower, but the view is just as good when you're out there......

From the Saturn page on the Wood's site Sailing Catamarans - Saturn - 8.8m hard chine performance cruiser with central cuddy

Totals:
10 sheets 6mm ply
52 sheets 9mm ply

A laminating table is much less likely to suffer weather damage than carefully aligned and set up frames and stringers, especially if it is partially sheathed in bare ply in variable humidity.
I have infused in sheds where the rain dripped through the roof onto the infusion. No damage. I have also abandoned hand laminates in the open when it rained unexpectedly. Then had to cut off the dry glass, feather the edges and scrub the cured resin with warm water to remove the blush and wait a week for the bare wood to dry. When I was selling epoxy (10 years), the most common application problems related to moisture on uncured laminate.

As I said above, the vac pump will cost a couple of hundred bucks, the bag, tacky tape and plumbing another couple of hundred. There will be more than that saved in resin, sandpaper and the tools needed to work ply compared to those required for infusion.

I cruised a 2 ton, 9m cat from the UK to Greece and back. I can assure you that half a ton on such a boat is not "a bit heavier" and nor will it only be a "bit slower". It will be harder to handle, draw more, be slower to tack, scarier to gybe, wetter, have more to scrub and antifoul, will need a bigger motor and will be significantly slower and less weatherly. This is why racing multihulls spend so much effort to reduce weight.

Owly,
Great that you are considering infused foam/glass. If you like, let me know when you are ready to start and I will see if I can help you save some time and money and advise on your infusion technique. I discovered yesterday that a guy I am advising on infusion and supplying some materials to is building a Saturn. I will keep you informed of progress.

Oryx (Pete Hill's cat) would seem to be a great deal for someone.

[Teleman]

Oooops!

You're right, 52 sheets of 9mm. for the whole boat. I was just looking at the hull quantities.

Definitely a significant weight difference, apart from the time required to fit and fair stringers and sand/fill/sand the whole thing.

I'm leaning towards foam, just wish it was cheaper. But then I wish everything was cheaper.............

[Redreuben]

175 kilos is 175 litres of water or 200 litres of Diesel, or several lockers stuffed with food, that is significant.

[owly]

Is it normal for posts to simply vanish into thin air on this forum? Did I offend a moderator? Is it illegal to mention suppliers by name? I finally found a supplier with affordable foam.... Divinicell H80 $97.17 for full 4x8 sheets in cases of 30, and fabric and resin at decent prices..... Fi__rgl__s Su__ly, located in Burlington Washington. Does one of the moderators own part of Ja__sto_n Dis___butors, or some other big supplier?

This pricing brings the cost foam building down to within a realistic range. I strongly resist being gouged on parts, materials, and equipment just because the use is marine....

The cost premium is minimal with this kind of pricing, and it is within driving range for me as I travel in that direction once a year to see relatives. I could carry enough materials on my pickup to build most of a boat shell. 50 sheets of 3/8 H-80 foam makes a stack less than 20" high and weighs in at 250 lbs...... I could carry that much on top of my Outback, with resin and fabric inside.....

With these kinds of prices, it would be silly to build the one of the boats I was considering in plywood. With payload being one of the highest priorities, this means that either of the two boats I've been looking at would easily meet my needs. To achieve the same payload in plywood would require a far larger boat, which is exactly what I do not want, regardless of Double-U's recent absurd statements about minimum size for couples and singles and anything under 30' being a "deathtrap"....

The other thing to consider here is that there would seem to be absolutely no reason why marine construction foam would need to be used throughout the boat. Obviously the hull sides and bottom, and structural members need to be 5 pound structural foam, but ordinary 2 pound extruded polystyrene .... the blue or pink stuff, has been used in aircraft building for many years successfully. The Rutan brothers, Burt and Dick, pioneered this in their EZ series aircraft, the main wing and canard wing both being blue foam hot wired to shape, with trenches for unidirectional roving for spar caps. I know of no structural failures, and hundreds of these have been built starting about 1980. Lower density means thicker foam can be used, which in turn means greater stiffness and strength for the same weight. It lacks much impact resistance, and lacks the ability to form around much of a curve without snapping on the tension side. It would work great for bulkheads and interior furnishings. The thinnest I can find is 1". It could also work well in parts of the bridge deck cabin, or even the bridge deck itself. Wherever it will not be subject to hitting docks and floating stuff, it could do the job. At 1/5 the cost of Divinicell, it would be foolish not to use it where it was appropriate. One inch foam with the same fiberglass on the surface is far stronger than 3/8. The strength is in the fiberglass........ Think OSB I joists..... The depth is where they get their strength.

H.W.

[rob denney]

Owly,

There is a bit more to cores than meets the eye. Maybe have a look at the harryproa chat group for a recent discussion on pros and cons. https://au.groups.yahoo.com/neo/grou...tions/messages

My last quote for 12mm/half inch D/cell was $Aus35.68 per sq m or $US80 per sheet. Your supplier sells it for $US121/sheet. If you keep looking, you may get it even cheaper. Or, if you don't mind mucking about with the shipping, I could send it from here.

If you simply
replace ply with foam/glass sheets you will have 6 full length joins per hull on the Kohler boat, 7 (or 9 with the knuckle) on the Woods'. These will either require the timber stringers and keels you need for the ply boat, or the panels can be filletted and glass taped, inside and out. The former requires a frame to support the stringers the latter ~720 ft (6 x 30 x 2 x 2) of filletting and tabbing, a fair bit of which will be on your hands and knees. This will not only destroy your back, it adds cost and weight and needs to be faired in afterwards. Plus you will need to do multiple infusions.

Intelligently Infused, there are two matching glued joins with no filletting, tabbing or fairing required and no need to set up the frames for each hull as they glue straight into the hull halves. You will need to build a simple, waist high, mdf mould which will be used for all 4 hull/deck halves.

[owly]

Originally Posted by rob denney

Owly,

There is a bit more to cores than meets the eye. Maybe have a look at the harryproa chat group for a recent discussion on pros and cons. https://au.groups.yahoo.com/neo/grou...tions/messages

My last quote for 12mm/half inch D/cell was $Aus35.68 per sq m or $US80 per sheet. Your supplier sells it for $US121/sheet. If you keep looking, you may get it even cheaper. Or, if you don't mind mucking about with the shipping, I could send it from here.

If you simply
replace ply with foam/glass sheets you will have 6 full length joins per hull on the Kohler boat, 7 (or 9 with the knuckle) on the Woods'. These will either require the timber stringers and keels you need for the ply boat, or the panels can be filletted and glass taped, inside and out. The former requires a frame to support the stringers the latter ~720 ft (6 x 30 x 2 x 2) of filletting and tabbing, a fair bit of which will be on your hands and knees. This will not only destroy your back, it adds cost and weight and needs to be faired in afterwards. Plus you will need to do multiple infusions.

Intelligently Infused, there are two matching glued joins with no filletting, tabbing or fairing required and no need to set up the frames for each hull as they glue straight into the hull halves. You will need to build a simple, waist high, mdf mould which will be used for all 4 hull/deck halves.

Rob:
I tried to send in a request to join your group, as I have no access to files, photos, etc, as a non member. I completely failed to pass the "captcha" test, trying at least ten different scrambled letter and number combos. It would not accept any of my answers, though I've been through the process many times..... I've never experienced anything like this before........ I wonder if this is Verizon's idea of a joke?? No wonder people are switching over to Groups IO......

I'm having difficulty visualizing building your simple entire half hull molds accurately. Obviously there must be a left and a right, and the parts are different height depending on weather it's an inner or an outer. The same supporting structure could be used for each left and right. I'm visualizing the bulkhead patterns being used to support the "simple" female mold, 30' long, the foam being laid into the mold. This would encompass every part of a half hull including half a bottom and half a coach roof. The entire thing would be infused, presumably including both the inside face and the outer face, though I'm not quite sure how one gets the resin to both faces at once, or how you monitor the progress of the resin on the side you cannot see? I would assume one would have resin ports on both faces, and vacuum all around the rim, and that the fiberglass would extend well beyond the foam.
The concept is quite intriguing. Having the hulls in vertical halves , makes the installation of the interior a piece of cake!!
In my fevered imagination, the bridge deck and bridge deck cabin including the bulkheads that join it all together are made on the floor, or a platform, the deck first, followed by the bulkheads and interior appointments. The forward portion of the cabin top, up to the bulkhead at the forward end of the saloon, being made in one piece and the aft portion being made in one piece also, both being final fitted and installed after the assembled hulls are joined to the bridge deck and bulkheads that join it all.
It all sounds like the stuff of fantasy to me ;-)

H.W.

[rob denney]

Originally Posted by owly

Rob:
I tried to send in a request to join your group, as I have no access to files, photos, etc, as a non member. I completely failed to pass the "captcha" test, trying at least ten different scrambled letter and number combos. It would not accept any of my answers, though I've been through the process many times..... I've never experienced anything like this before........ I wonder if this is Verizon's idea of a joke?? No wonder people are switching over to Groups IO......

No problem from this end. It's good to see you contributing there.

Originally Posted by owly

I'm having difficulty visualizing building your simple entire half hull molds accurately. Obviously there must be a left and a right,

My apologies. I was thinking harryproas, where there is only one mould per hull; sometimes one for both hulls, and on the latest, the same mould does both hulls and the cabin top. You will need 2 moulds, but the frames and lining from the first one can be used for the second.

Originally Posted by owly

and the parts are different height depending on weather it's an inner or an outer. The same supporting structure could be used for each left and right. I'm visualizing the bulkhead patterns being used to support the "simple" female mold, 30' long, the foam being laid into the mold. This would encompass every part of a half hull including half a bottom and half a coach roof. The entire thing would be infused, presumably including both the inside face and the outer face, though I'm not quite sure how one gets the resin to both faces at once, or how you monitor the progress of the resin on the side you cannot see?

That is how we do it, but it gets tricky at changes of direction, ie chines, bows, transoms. If there is any gap in the core, it fills with resin. There may also be difficulties with curvature. If the foam doesn't sit flat on the mould pre vacuum, there wil be gaps.

The foam is scored (2mm x 2mm scores) and perforated. The resin travels the length of the mould in a piece of spiral cut hose and feeds sideways into the scores and through the perforations to the laminate below. If you do your first test on a pices of glass or perspex, you can watch the resin front on both sides.

Originally Posted by owly

I would assume one would have resin ports on both faces, and vacuum all around the rim, and that the fiberglass would extend well beyond the foam.

No. Resin port at one end, vac outlet at the other, with a bleeder around the edge. The fiberglass ends at the core edge, there is no cutting or grinding post infusion.

Originally Posted by owly

The concept is quite intriguing. Having the hulls in vertical halves , makes the installation of the interior a piece of cake!!

Sure does. The only part of the boat building that is easier than installing the interior is wetting out the hulls and the interior.

Originally Posted by owly

In my fevered imagination, the bridge deck and bridge deck cabin including the bulkheads that join it all together are made on the floor, or a platform, the deck first, followed by the bulkheads and interior appointments. The forward portion of the cabin top, up to the bulkhead at the forward end of the saloon, being made in one piece and the aft portion being made in one piece also, both being final fitted and installed after the assembled hulls are joined to the bridge deck and bulkheads that join it all.

Pretty much. except that it is easier to build a table (couple of pieces of mdf on sawhorses) so you are working at a comfortable height.

Originally Posted by owly

It all sounds like the stuff of fantasy to me ;-)

It is, until you try it and see how easy it is.

[downunder]

Only,

would be worthwhile looking over Derek Kellsal's website for thoughts on foam infusion.

Catamarans - Kelsall Catamarans - What is KSS?