Wondering what difference between this 2 different cat designs

[billgewater]

Some catamarans e.g. the splendid Crowther cats. had expanded aluminium mesh foredecks. Probably not all that comfortable to walk on, but I have never seen an owner remove these foredecks. Some cats also have used expanded aluminium for the aft decks. and for probably the same reasons. Solid to walk on, but let water and air through readily.

[fxykty]

Our cat has very long tramps. In our yacht manual it specifies a minimum openness of 75% when replacing the trampolines - that rules out anything other than relatively open net. The main reasons for this are to not catch air underneath when cresting a wave and to not add weight with caught water. Both conditions could contribute to pitchpoling or capsize. This applies to some greater or lesser extent to all catamarans, but presumably cats with very dense mesh style tramps or solid decks were designed that way on purpose and with good regard towards safety.

Our nets are strung very taut and are no problem to walk or work on. We lay lounger cushions (from outdoor deck sun loungers that we bought cheap and use as extra long-length cockpit cushions) on the tramps when we want to relax without getting a grid pattern on our skin. They’re a super place to star, bow wave, dolphin, and general life watching.

[Dave_S]

I changed my tramps to 25mm square netting with 3mm cord (very open) from solid woven with maybe 4mm holes with 8mm flat material (very closed).

It used to pump mist and spray forwards over the swell and now it doesn't and the tramps would bellow up and suck down as we went.

I am quite sure that the boat performs better now the air under the boat can get out freely.

So I am on the pro netting side of the discussion.

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I was going to leave this bit below out because it may be misleading but it is interesting. (well for me anyway, but I may have some form of sickness)

I can point further to windward by about 4-5* apparent.

CAUTION: I made 3 changes at the same time. I know I should have made one change at a time but it didn't work out that way. Less weight, took the reacher down from in front of the jib, and changed out the netting.

The biggest change was probably from the taking the reacher down when heading to wind but I'm sure the netting participated. I can easily test that.

[Symphony]

I mentioned in other threads about my Atlantic delivery of a Bali 40 but some of it bears on this thread. The Bali has a solid foredeck with a sunken conversation pit and table.

We were caught in a gale for a while with 10-12’ seas. The deck and conversation pit would ship a lot of water. We never pitchpoled but dug a few wave faces since the weight of water would overwhelm the very buoyant bows. I never felt in danger from those few times.

The many bombs / slap were all caused by the bridge deck and I don’t think the foredeck caused a louder noise or impact, at least for us in the bridgedeck.

The most negative aspect of the solid foredeck was that all the water up there was directed back and forth between hulls and eventually aft down the side decks. A lot of water. The cheap plastic hatches leaked constantly - all beds were horrid.

I am sure the charter guests enjoyed it on calm days!

Every design feature has a purpose and a drawback.

[markpierce]

Frequently have steep five-foot waves here in the San Francisco Estuary likely to pound the pants off such a catamaran.

[Symphony]

Originally Posted by Dave_S

I was going to leave this bit below out because it may be misleading but it is interesting. (well for me anyway, but I may have some form of sickness)

I can point further to windward by about 4-5* apparent.

I am certain reducing the windage makes the boat faster and point higher.

I used to wonder just how much advantage the racers got with the skinny carbon stick and rod rigging - I wondered until I delivered an Amel 53 with fat short masts, super oversize rigging wire, oversize fat headstay, oversize frames on the standing rigging, and that all made a drastic reduction in upwind speed and angle. I could feel the air hitting us in all those places like a drag net. Of course, the Amel is designed to be a great DOWN wind boat naturally.

[riki]

Originally Posted by belizesailor

The forward nacelle on a Privilege doesnt normally get any wave slap...could in really ugly seas, but not a practical issue. The slap/pounding typically encountered on cats is under the bridge deck. Privileges have good bridge deck clearance so typically not a problem either...though the bridgedeck, not the nacelle, is where it will slap in the right conditioms.

Privileges do NOT have a solid foredeck BTW...just smaller nets either side of the nacelle. They are down in a bit of a hole as a result which means the foredeck is uneven (ups and downs).

The forward nacelle has a v-hull like shape so cleaves any waves that should get that high. It also creates additional storage space...and another cabin on bigger Privileges...a big one on the 65.

Some Privileges Ive run tend to sail at anchor a little when the wind picks up. Not something a cat normally does. My hypothesis is the nacelle acts like the bow on a mono and causes this (its minor, but noticeable if you are on the foredeck).

Thanx for the info.
Agree that Privilege might not be the perfect example as a solid forward bridgedeck but probably somethinh in the middle:

[riki]

Thanx to you all for chiming in and provide all the usefull info. Much appreciated.
cheers

[danielamartindm]

Just MHO. I've never sailed a cat with a solid foredeck; but I have sailed some rough seas with tramps. I think the popularity of tramps on cats arose from considerations that were more theoretical than practical. It's the bridge decks that slam, and I've very rarely seen an actual wave (I'm not talking spray) crash up through a trampoline. I think you'd have to be very overpowered or bow-heavy for that to be an issue. Tramps are degraded by salt and UV and need to be replaced, a flaw not shared by solid foredecks; but with a tramp, water taken aboard forward is efficiently gone very quickly. I really don't like the instability of tramps when you walk on them, and I avoid doing so when ever possible- but solid decks can be slippery. No design is perfect, I guess.

[riki]

Originally Posted by danielamartindm

Just MHO. I've never sailed a cat with a solid foredeck; but I have sailed some rough seas with tramps. I think the popularity of tramps on cats arose from considerations that were more theoretical than practical. It's the bridge decks that slam, and I've very rarely seen an actual wave (I'm not talking spray) crash up through a trampoline. I think you'd have to be very overpowered or bow-heavy for that to be an issue. Tramps are degraded by salt and UV and need to be replaced, a flaw not shared by solid foredecks; but with a tramp, water taken aboard forward is efficiently gone very quickly. I really don't like the instability of tramps when you walk on them, and I avoid doing so when ever possible- but solid decks can be slippery. No design is perfect, I guess.

No design is perfect, i agree. The fact that some new designs are going solid deck again just demonstrate this and that at the end of the day it's just a matter of taste and trends.

[rbrentp]

I have a Prout - solid foredeck, I have had two with tramps. Slam is bridgedeck height. What I can say about tramps is, pleasant easy cruising, with padding for a resting paradise. The Privilege designer like tramps but hated walking on them, hence the hard walkway. Having spent time on tramps in active weather and needing to attend to a furler while balancing on ropes, etc. is not a joyful experience. Slip through one time and you will be a believer. Of course if you have really big wide feet, it is probably not an issue.

[fxykty]

Originally Posted by danielamartindm

Just MHO. I've never sailed a cat with a solid foredeck; but I have sailed some rough seas with tramps. I think the popularity of tramps on cats arose from considerations that were more theoretical than practical. It's the bridge decks that slam, and I've very rarely seen an actual wave (I'm not talking spray) crash up through a trampoline. I think you'd have to be very overpowered or bow-heavy for that to be an issue. Tramps are degraded by salt and UV and need to be replaced, a flaw not shared by solid foredecks; but with a tramp, water taken aboard forward is efficiently gone very quickly. I really don't like the instability of tramps when you walk on them, and I avoid doing so when ever possible- but solid decks can be slippery. No design is perfect, I guess.

Well, on passages between New Zealand and the South Pacific Islands, which is an 1100-1300nm distance roughly S-N and can be a reach or close reach with lots of wind and sea state to match, we’ve often had solid water come up through the trampolines. Downwind not so much, but reaching and hard on the wind absolutely yes. Our life raft used to be mounted in the corner of the front trampoline, where the main beam intersects with the hull. During our last passage south that life raft was torn away and lost by the water coming through the tramp. Now we’re considering whether to replace it but if we do it’s going in a cockpit locker with a new hatch in the bottom.

My point is that trampolines, and their sizes, as well as the evolution towards smaller or no tramps and hard foredecks, is a deliberate design decision and trade off between sea keeping ability and accomodation spaces. Originally trampolines were used to bridge open spaces with the lowest possible weight so people didn’t fall through. Cruising designers started filling in those spaces with decks and accommodations. Those aren’t generally assets for sailing and sea keeping ability but definitely increase liveability.

Contrast that photo of the large Privilege (is it the same as the one the Sailing Zatara guys have got? They’ve got a whole cabin up front there!) with this photo of our boat.



You pick what’s important to you and you love your choice. When used as intended it’s perfectly capable and safe. Beyond that, probably still safer than driving a car.