Woods Designs & Bridgedeck Slamming

[Barra]

Well said Uncivilised - spoken like a true sailor. Too many cruising cats are sold and bought based on dockside appeal not sailing ability which sadly reduces the number of good sailing cats out there but they are out there. BD is a compromise like all the characteristics and you can achieve a better set up if you decide you dont need 6'5 of saloon headroom for sure.

Re the BD slamming in my experience all cats slam at some point - its just a question of getting the right conditions. Our current 42 foot boat has 68cm BD clearance at CWL but only 48cm at the nacelle which runs all the way to the BD stern catana style (2 feet and bit less than 1 1/2 feet respectively) ie I can run a tender under either side of the nacelle but wouldnt be able to get under the nacelle. So Ive kinda got both worlds under my bridge deck.

We get some tickles on the nacelle pretty regularly in typical seastate generated by around 21 knots TWS if going to wind. In beam conditions its determined by the sharpness of the wave faces vs the width between hulls ie sharp waves of over 3 feet can hit that nacelle again but 12 foot longer period waves dont touch. Downwind we are yet to slam in anything.

The worst we had where we actually got true BD slamming not just the nacelle was when we had waves from 3 different directions from different weather systems that would occasionally meet between the hulls. Every 10 minutes or so it would shake the hell out of the saloon table - not alot of fun - but there was no way another foot or more of BD clearance would have made any difference to my mind in those conditions (nor a course change)

So for a 42 foot cat with foot and a half clearance yes you will get some slamming in the conditions I mention but with the 2 foot of the rest of my BD its a rare thing. Open ocean with longer period waves arent really the issue its the short sharp coastal stuff that can cause concern.

Just like a thin hulled racing mono you get used to the noise though and the performance more than makes up for it and its rare enough that even at 1 and half feet I wouldnt be too worried.

[Sos]

Here is a blog of a Sagitta that crossed the Atlantic.

[junek]

Look into Schionning Designs. They are designed for sailors like you that don't want to trade performance for over-the-top interior space and comfort.
The Wilderness 10.30m or 11.20m may suit your needs.
I wouldn't want to do serious passages is a cat with anything less than 600mm (2foot) BDC. Ideally, more like 750mm+

It is of course your decision, but I would never build or buy a 30foot+ cat that does not have ample standing headroom on the bridge deck. If for no other reason than for the fear of resale time....noone will want it. And there are plenty of other reasons (for me!).

Hope you build the right boat. I plan to build a Schionning Wilderness 12.5m or something similar in the future.

[UNCIVILIZED]

Thanks for the help guys, Really. And Barra, your description of your boat & what kind of conditions it take to make her slam is perfect. Thank you! I'd love it if a dozen other catamaran owners would chime in with a similar level of details. Not to mention favorite designs & why, even if you've only "borrowed" said design for a test sail/vacation. And are now building one for yourself.

Ah, and everyone have a great weekend. Be it here, on the forums [giving me info ;-) ]. Or out in the real world, playing with your toys in Neptune's realm!

[UNCIVILIZED]

Does anyone else care to chime in with a bit of wisdom on this, please?

[RKsailsolo]

Originally Posted by UNCIVILIZED

Does anyone else care to chime in with a bit of wisdom on this, please?

Good topic, having cat owners describe the condition when their boats start to bridge deck slam, but it's no doubt a sensitive one. In the spirit of learning and this series of Cruiser forums, maybe consider opening up this topic as a new one that is written in the manner that makes it "safer" to share their experience.

[Grateful]

Uncivilized,

It's good to see someone prepared to think out of the box. We all know that each facet of boat design includes a compromise. I don't think you mentioned the intended use for your new boat. For a day sailor / 'round the buoys / weekender I think that your criteria are pretty spot on. If you intend to do extended cruising, your comments prompt couple of observations:

Elevated helm station. You stated a preference for avoiding an elevated helm station. I certainly understand the theoretical drawbacks of windage, difficulty of getting to and from, and increased motion further from the waterline. In fact, a well designed elevated helm position isn't all bad. I certainly appreciate the excellent view of sails and the area surrounding the boat and in all but the most horrific sea states (when I'm likely to be letting auto do most of the work anyway), the motion is no big deal.

Reduced headroom in the bridge deck area. If the boat is set up galley down, (as is the case in the Curt Hughes design), I suppose one could live with reduced headroom for using the nav station, eating, and lounging in the salon. There is, however, a lot to be said in favor of a galley up configuration both under way and at anchor, and that's not practical with reduced headroom. Passing food and drink up from below and being sentenced to the galley dungeon isn't so nice compared to cooking, eating, and socializing all on one level.

May I be so bold as to suggest that you consider chartering one of the popular boats for a week and see what I mean about what has evolved to be 'standard' features of the production cats? Personally, despite being a recovering racer; for cruising and living aboard I am willing to give up 10% of theoretical performance in exchange for a the very comfortable living situation afforded by a Lagoon, FP, or similar boat.

(Flack jacket on for the inevitable replies from more performance oriented sailors )

[Barra]

Ok Grateful Ill bite -

Its alot more than 10% improvement in performance thats gained through the compromises to lower windage, especially where windward performance is concerned. I was lucky enough to have a few sundowners with a lagoon 450 owner a few months back who was honest enough to admit that he was over the moon if he could point at 60 degrees and the norm was more like 70. All that windage from whats effectively 3 stories on water.

Meanwhile we tack through 36 degrees and when we get a better heady next year that should come up further (the sail is limiting us not the boat design). Our compromise to do this is the extra cost of daggerboards and a saloon with a step down from the cockpit. We still have 6 foot 2 headroom though that comes down to 6 foot at the side and full views from the saloon (we arent a mono - just the one step down). And we have galley up. The extra plus is it lets us see forward over the saloon from the cockpit as well. Since we have aft helms this is pretty handy if the weather is foul as we can keep a forward watch from either the saloon or the cockpit.

Its a catana design and its been interesting to note that even they are moving away from the step down saloon thus costing performance but increasing dockside appeal to some.

Everyones got a different set of priorities but to us thats a very small compromise to actually be able to sail our boat to wind instead of talk about performance just in relation to reaching. Sailing to wind in our boat is a ton of fun. If I could only point at 60 to 70 degrees I would sail a whole lot less and enjoy cruising a whole lot less.

That said we had the sundowners on the lagoon 450 as that was the most comfortable for a crowd

[colemj]

Originally Posted by Barra

Meanwhile we tack through 36 degrees

I assume you mean that you tack through double that number - and that number represents apparent wind?

No way you tack through 36*, and it is highly doubtful you tack through 72* true.

I have sailed a Catana 401, which is almost identical to yours and they are nice upwind boats for sure.

Just not that nice…

Mark

[Barra]

Originally Posted by colemj

I assume you mean that you tack through double that number - and that number represents apparent wind?

No way you tack through 36*, and it is highly doubtful you tack through 72* true.

I have sailed a Catana 401, which is almost identical to yours and they are nice upwind boats for sure.

Just not that nice…

Mark

Yes i am talking apparent wind angles in case that wasnt clear ?

as was the lagoon 450 owner.

If youve sailed the 401 then you know 36 apparent is completely doable and since we bought the boat with a 150 genoa im pretty sure it will point higher once we move to a jib and reacher combo as should have been the case from the start.

[Boatguy30]

The Vardo clearance is 20" at the hull sides and 18" on the CL as the underside of the bridge deck is slightly V'd. This is at full load displacement of 11,000 lbs. my boat floated roughly 6" high of this when launched with mast, engines, sails and all other basic gear.

the Eclipse and Sagitta are really no full cruising designs. The Eclipse is marginal for long range cruising as it has less than a 1 tonne payload with an average build and fit out.

So 18" is maybe not fantastic, but it is a small boat and that lowest area is only 8' long. There is a Norseman 500 in my harbor with about the same clearance with about a 20' long bridgedeck.

[Dulcesuenos]

Boatguy, got pics anywhere?

Sent from my LG-LS980 using Cruisers Sailing Forum mobile app

[Grateful]

Barra,

Wow, that's some performance to weather!

Actually, I count the Catana boats as among the "modern production boats" with full headroom and galley up vs some of the frankly odd ball designs from Australia and the US West coast. I have to ask though, how did you like getting to and from, and sitting in that helm position in a very big following or beam sea off shore? That always seemed to me to be a wet, dangerous place to be unless you are just sailing around the bay or between islands.

I've never been on a Lagoon 450 (On paper they look heavy, under powered and, as you mention, have terrible windage.) I did spend some time and several thousand miles on a Lagoon 400 and was very impressed by it's performance.

(Kurt, if you're reading along, we sailed together on the University of Puget Sound sailing team and on that God-awful blue SJ 30 way back when - please don't take offense!)

[Southern Star]

Uncivilized, the PDQ 32 had a great way of dealing with the lack of full headroom in the bridgedeck saloon of a smaller cat - a large sliding hatch with a removable canvass enclosure that permitted full headroom for access to the hulls when open. Perfect when at anchor or, without the enclosure in place, for sailng in reasonable conditions.

I know that it is your intention to build a new cat, rather than purchasing a used one, but perhaps you could incorporate that into your design. You may also want to see if you can get the owner of a PDQ 32 to take you out for a test sail. The boats had decent bridgedeck clearance, relatively low windage and are in the range of size that you are looking to build. At least it may give you an idea of whether that size and type of design will work for you.

Brad

[Oliver L.]

Uncivilized,

one more statement for your stats, albeit with a slightly larger boat. Our clearance is about 75 cm, which means that I can slide through with the dinghy easily. And still we do have bridgedeck slamming. It just takes a bit worse weather.

However, what I really want to point out to you is that on most crossings the bridgedeck is not nearly as bad as the slamming the two hulls get when you're not sailing straight downwind. In the aft cabins you are really in the centre of a very nice drum that gets a beat every few seconds. Many times in bad weather it sounds as if the boat would disintegrate the next minute, while in the salon or in the cockpit it is much less noisy.

...and as to the comments regarding tacking, on flat water with full sails we have tacked about 80 degrees on the chartplotter. But then, that's one reason why I love the 470 so much more than the 440 or 450... it's still mainly a sailboat...

Oliver