Bridgedeck clearance - small cat

[Be Free Sailor]

Hi
I previously sailed Lagoons 440, 410 and 380 and now I am looking to further reduce my upfront cost of buying a boat, and at the same time I want to increase the waterline length and reduce windage/weight Problem is the cats I like, that are also in my price range, they do not have much bridgedeck clearance at all. Having offshore sailing experience with Lagoon 380, I did have a very noisy life aboard when going 60 degrees into waves in the Biscay with winds 30-35 knots, but other than that I think it was OK. Even the 440 was very noisy in a beam on 30-40 knots wind and waves in the Med...and the 410 was more noisy than the 380 due to the "box" design of the underside of the bridgedeck - Lagoon made room for a transverse bed in the aft cabins, hence the square sticking out under the hull - very noisy!
The boat I am looking at is a 39 foot South African designed (Simonis) catamaran, which has a slightly lower bridgedeck clearance than the Lagoon 380. I talked with an owner who did 2 circumnavigations on an identical boat, he did not think it was any problem at all, and he loves his boat.
I know it is hard to make any advice on such matters, but perhaps someone did offshore sailing in one of the "old" Leopards which I believe was also Simonis design, with pretty low bridgedeck clearance. Downwind I am sure everything is great, and not problems there...am I correct in this assumption? And I assume it is going to be noisy going upwind, something I always did try to minimise anyway in my Lagoon, but did enjoy when there were no big waves...but in reality is there that much difference going upwind in a Lagoon vs e.g. an old Leopard 38/40, when comparing the slamming of the bridgedeck?
The clearance for a Lagoon 380 is around 75 cm (2,5 feet) if I remember correctly, and for a Simonis 38/40 foot boat, like the one I am looking at, the clearance is around 55 cm.
Apart from looking a bit odd, when viewing the new boat from behind, I am not really sure if it should be a deal breaker.
I am looking at a cheaper boats than the previous Lagoon 380 I owned, and I like the design of the older Simonis designed boats. Also many are better built then a Lagoon, where some of the manufacturers (well, actually I would tend to call them boat yards) are using closed cell foam core instead of balsa, and fully tapped in bulkheads etc, making it a nicely built boat, I think. Strangely enough, these much better built boats cost less than a Lagoon 380, but of course there is much less "apartment" feeling / less volume inside, but then again better saling ability - less windage, less weight a.s.o.
Any thoughts or comment, please feel free to share
Thanks!

[Tupaia]

What boat are you considering?


For some unknown reason both Simonis and Lavanos's older designs especially the small sizes have truly awful bridge deck clearance. Seemed to be the trend in SA a while back. Provides for less windage and a lower profile on a smaller cat but with very reduced under wing clearance. So much so that a bad sea state will make going to windward a real chore. Probably the only exception I can think of is Scape by Simonis. Try, in less than optimal conditions before you buy.

[beta600]

Originally Posted by Be Free Sailor

Hi
I previously sailed Lagoons 440, 410 and 380 and now I am looking to further reduce my upfront cost of buying a boat, and at the same time I want to increase the waterline length and reduce windage/weight Problem is the cats I like, that are also in my price range, they do not have much bridgedeck clearance at all. Having offshore sailing experience with Lagoon 380, I did have a very noisy life aboard when going 60 degrees into waves in the Biscay with winds 30-35 knots, but other than that I think it was OK. Even the 440 was very noisy in a beam on 30-40 knots wind and waves in the Med...and the 410 was more noisy than the 380 due to the "box" design of the underside of the bridgedeck - Lagoon made room for a transverse bed in the aft cabins, hence the square sticking out under the hull - very noisy!
The boat I am looking at is a 39 foot South African designed (Simonis) catamaran, which has a slightly lower bridgedeck clearance than the Lagoon 380. I talked with an owner who did 2 circumnavigations on an identical boat, he did not think it was any problem at all, and he loves his boat.
I know it is hard to make any advice on such matters, but perhaps someone did offshore sailing in one of the "old" Leopards which I believe was also Simonis design, with pretty low bridgedeck clearance. Downwind I am sure everything is great, and not problems there...am I correct in this assumption? And I assume it is going to be noisy going upwind, something I always did try to minimise anyway in my Lagoon, but did enjoy when there were no big waves...but in reality is there that much difference going upwind in a Lagoon vs e.g. an old Leopard 38/40, when comparing the slamming of the bridgedeck?
The clearance for a Lagoon 380 is around 75 cm (2,5 feet) if I remember correctly, and for a Simonis 38/40 foot boat, like the one I am looking at, the clearance is around 55 cm.
Apart from looking a bit odd, when viewing the new boat from behind, I am not really sure if it should be a deal breaker.
I am looking at a cheaper boats than the previous Lagoon 380 I owned, and I like the design of the older Simonis designed boats. Also many are better built then a Lagoon, where some of the manufacturers (well, actually I would tend to call them boat yards) are using closed cell foam core instead of balsa, and fully tapped in bulkheads etc, making it a nicely built boat, I think. Strangely enough, these much better built boats cost less than a Lagoon 380, but of course there is much less "apartment" feeling / less volume inside, but then again better saling ability - less windage, less weight a.s.o.
Any thoughts or comment, please feel free to share
Thanks!

not so much the clearence,, the deck house forward is mostly the problem,,,

[Be Free Sailor]

Originally Posted by beta600

not so much the clearence,, the deck house forward is mostly the problem,,,

no comprende...?

[Johan Leopard51]

I think the science about bridgdeck and hull shape in cats is evolving. For example on Leopard 51 and 53 the new 53 powercat has a noticeably different bridgedeck seen from the front. It is almost like a wide round bow whereas our 51 was very slimline like a slab for first few meters. For sure the height from water to the area under cross member at bow on 53 is far less than our 51. That design seems very deliberate.

(It could also be structural because some 51 had structural cracks of the member between the two hulls at bow - we strengthened ours after some cracks appeared)

If you google leopard 51 and 53 and click images you’ll see what I mean. The thinking is probably to “take” the wave earlier rather than under saloon and combine that with that the hulls are more parallel under saloon as opposed to having two symmetrical hulls that create a funnel which invariably causes a slap at the narrowest point which is under saloon.

So I’d look at hull shapes as much as physical clearance and if there is going to be wave slap, that this happens forward of the saloon rather under it.

[Be Free Sailor]

Originally Posted by Johan Leopard51

I think the science about bridgdeck and hull shape in cats is evolving. For example on Leopard 51 and 53 the new 53 powercat has a noticeably different bridgedeck seen from the front. It is almost like a wide round bow whereas our 51 was very slimline like a slab for first few meters. For sure the height from water to the area under cross member at bow on 53 is far less than our 51. That design seems very deliberate.

(It could also be structural because some 51 had structural cracks of the member between the two hulls at bow - we strengthened ours after some cracks appeared)

If you google leopard 51 and 53 and click images you’ll see what I mean. The thinking is probably to “take” the wave earlier rather than under saloon and combine that with that the hulls are more parallel under saloon as opposed to having two symmetrical hulls that create a funnel which invariably causes a slap at the narrowest point which is under saloon.

So I’d look at hull shapes as much as physical clearance and if there is going to be wave slap, that this happens forward of the saloon rather under it.

Yes my previous Lagoon 440 did have a "wave breaker" in the middle / front of the bridgedeck, and I believe that helped...

[Rohan]

Originally Posted by Be Free Sailor

Yes my previous Lagoon 440 did have a "wave breaker" in the middle / front of the bridgedeck, and I believe that helped...

Is "wave breaker" the word for it? I don't know if there is even an official term. But I'm sure you mean something like this:

https://nara.getarchive.net/media/th...9b83?zoom=true

https://www.boatdesign.net/attachmen...ck1-jpg.59259/

If you find a cat you like otherwise, I wonder if it's possible to securely add something like that to the hull?

[Tupaia]

Originally Posted by Rohan

Is "wave breaker" the word for it? I don't know if there is even an official term. But I'm sure you mean something like this:

https://nara.getarchive.net/media/th...9b83?zoom=true

If you find a cat you like otherwise, I wonder if it's possible to securely add something like that to the hull?

This is a wave breaker, but not quite the same. Powerboats are typically much narrower than sailing cats. When 2 hulls run close together the wake from each meets at some point and creates a standing wave if the bridge deck is low and the hulls are close enough together this wave would constantly impact the underside of the bridge deck and cause drag, regardless of the sea state.



Ideally on a sailing cat this wake convergence should occur after leaving the tunnel, at the stern of the boat. Some sailing cats with low bridge deck or one that is more forward use a similar appendage to mitigate slamming when going to windward. The underside of the bridge deck is often arched to redirect the waves. Retrofitting such an appendage is likely to be very heavy and cause unknown stress areas.

[beta600]

Originally Posted by Be Free Sailor

no comprende...?

the wheel- house act as a resonance case..

[Sos]

Some info on bridgedeck clearance

.

We have a woods designed cat that has low clearance but the wide beam helps. We get some slamming but it's never been a problem with our sailing in the Solent and the English channel. However always try and avoid upwind when possible

[Tupaia]

Originally Posted by Sos

We have a woods designed cat that has low clearance but the wide beam helps. We get some slamming but it's never been a problem with our sailing in the Solent and the English channel. However always try and avoid upwind when possible

Old saying goes "Gentlemen never sail to windward" (applies to mono's too)


The wake angle is fixed at about 20 degrees so the wider the hulls are spaced apart the further back the convergence wave occurs. Closely spaced hulls with low bd is bad. Some cats are slow low the wake itself contacts with the bd.


Beating to windward in heavy seas we once drove the furling drum up the foil, still no slamming as our bd starts 3 plus metres from the bows and is high. My wife made me slow down.

[Be Free Sailor]

...well, I guess there is only one way to really know...I bought the boat and will find out next week, as I take her across a patch of 360 miles open sea

[Chotu]

nice! Congratulations!!

there is one forgotten factor that usually I bring up but it hasn’t been brought up in this thread yet.

The weight of the catamaran makes a big difference.

i’m assuming the lagoon that you have experience on has a much larger displacement than the one you just bought.

even with a higher bridge deck, if a boat has significantly higher displacement, it’s going to plow through the waves more than others, bringing the waves up closer to the bridgedeck. (or more accurately, the momentum will hold the bridge deck down near the waves)

if your boat is a lot lighter, just imagine a piece of Styrofoam shaped like a catamaran, the waves will never touch the bridgedeck no matter how low because the boat goes up over them.

to me, this is a very important situation to consider. It’s not all just static stuff. There is dynamic momentum and buoyancy involved in slamming