Bridge Deck Clearance . . . How Much Have You Got ?

[Dulcesuenos]

I agree with what Talbot says regarding hull design, Not sure if there is a boat that is any lower to touching then our endeavour, but the design of our central nacelle breaks the wave and the hull channels the energy and sends the wave down and out the back, sure we can pound easier going to windward, but its not a hard slamming its kind of a gentle thump.
Nacelle tank all the way, until I can afford a gunboat. >

[John Webb]

Ha ha..call ahead and get them to lift the bridge..

[John Webb]

Hi Talbot, I totally agree with your last post
consider ALL the factors rather than just "good bridge deck clearance = good"
Time for bed ..Night all

[Clipper4730]

Thanks everyone for the great responses, not to worry bridgedeck clearance is not the determining factor in our choice merely one more attribute that will help us choose the right cat. We have a spreadsheet of sorts with likes and dislikes of each boat. Ideally we would take the best attributes and incorporate those into a custom boat, unfortunately our pockets are not that deep. Any of the aforementioned would be suitable and in the end it will probably come down to price, condition, and location.

Thanks again

Will

[webejammin]

We found that the bridge deck pounding might slow our Gemini 105Mc some and the noise is a little un-nerving at first untill you realize the bottle of water on the table only shakes a little but doesn't move. There are advantages our little cat has like: only paying for a std 40 ft slip anywhere, like going under bridges with our 50 ft bridge clearence, price for what you get in a multi hull. We bought our 01 Gemini a year ago and love it, yes were sailing mostly on the Columbia river lakes and go out on the open ocean some but when the weather and conditions are bad we snug in and waite out the weather like most sailors. We think we have a great intro catamaran and replaceing it with a catamaran that doesn't have bridge deck slamming is about 4 times the price we paid. I guess you really get what you pay for.

[limejucer]

Dragon lady
my firts trip in limejuicer was plymouth to bristol round lands end in November with a weather window of F6 on the nose . seas never got much over 3m but hardly flat. with the nacelle there was little slamming (one lould one) but plenty riding up and down. when we turned and headed NNE She ran along beautifly with gusts near F8

A safe comfortable slow tank. O yea for the others she may be narrow but apart from one special ultra light racing variant i havent ever heard of a Snowgoose capsizing
a true blue water boat for the old and slow.(me that is)

[Ozbullwinkle]

Originally Posted by colemj

I don't know the exact numbers, but I can rank them from greatest clearance to lowest for you based on experience with each (except the new L39):

FP Lavezzi
Lagoon 410
Leopard 39
Voyage 43

Mark

Here is a clip that I took last week to specifically show the good bridgedeck clearance on the Fountaine Pajot 40 foot Lavezzi during a 500 Nm delivery trip from Mooloolaba in QLD Australia to Pittwater NSW.

Bridgedeck Clearance - Fountaine Pajot Lavezzi 40 - YouTube

The boat did everything that we asked of it including a moonless night where we had up to 40 knots but this was at 120 apparent. It was very comfortable during the trip in a variety of conditions.

[Tomahawk]

We nad a FP LVessi.. the hul form was very good for avoiding bridge slap..

However, it sailed like a brick... The boom is so high you need climbing gear and a safety harness to zip up the sail bag!!
And it had the pox after three years..
On the other hand it is a lovely marina or anchorage boat..

[Dragon Lady]

Hi Tomahawk,

Did you have a canopy on your Lavezzi?
I can't image what it must be like to unzip the sail bag without one.
I agree in light airs the Lavezzis are not the best but when the wind gets up they are fine.
We generally only experience occasional slapping in heavy seas, certainly in mild stuff like the video it is fine.
How do you find your Outremer compared to the Lavezzi?

[Tomahawk]

They are totaly different boats..
The Lavessi is a great boat for being at anchor and entertaining lots of people. However, it has huge windage and very little by way of centre boards and only goes well down wind.. with far too much wind for comfort.. It is too heavy with too much wetted area to make use of Gennaker as it will not get up the speed to cover playing the longer distances of gybing down wind...

The Outremer is like an old fashoined sports car.. it goes like .. well very fast... Think a 66 Musthang or Lotus Elan+2. It does not have the fancy fit out or much spare room... However at only 40 feet we can easliy handle the sails between two.. WhenI pull the tiller.. not a wheel.. the bow moves.. I can mTchnwind speed with boat speed up to about 12 kts of wind!

If you are thinking about a Lavessi.. get a very good Osmosis check.. it seems they had a problem with a few ..
Sadly they do not make the old style Outremer 40 any more as it is as expensive to build an old design 40 as a new design 50 ft..

[trinescape]

Hi clipper4730, on our 36' trimaran we have 700mm clearance at the bow and 650 at the stern we have had bridge deck slapping but only when sailing to windward in big seas or when you have two or more wave patterns and when they get together whamo ! you get thumped ,but generally we don't suffer from it ,I have read many posts on this subject and the general rule of thumb seems that 600mm is a minimum bridge deck clearance that you should seek from your catamaran good luck with your search cheers Andy

[Mark Johnson]

IF you want a serious "cruiser", and not just a marina bound condomaran, then you will need to be able to handle considerable amounts of going hard to windward, often in a gale. Survival storms will eventually be served up as well! I've been through more than a dozen hurricanes for example...

MOST, (but not all) FRP production cats are/were built to a design that does NOT fill these requirements, and they were NOT intended for this service. You need to pick from the <10% that were, NOT a belly dragger! ALL sales propaganda and claims from biased owners, that fly in the face of good naval architecture, should be ignored.

A true "cruising cat" has really good wing clearance for one, (enough to drive a high bow RIB through the wing tunnel). It needs to be wide as well, for stability.
(I know of Prouts for example, that I surveyed and found to be rather flimsy in construction. Due to their low wing clearance design flaws, they were driven back to the boatyard for months of repairs, after the first attempt to drive them into 35 knots of wind, and 8' seas)! The Gemini is similar... They and their type, are NOT the boats for this! Getting lucky only works for a while...

A good SEA BOAT would have JUST enough head room in the main bridge deck cabin, that you don't hit your head, and a cabin that is small, leaving GOOD visibility forward, (UNDER a high clewed jib), AND good walking space on its side decks.

It is thus designed to have relatively low windage, and applying these parameters, light but STRONG construction techniques & materials, AND low down locations for tools, tankage, engines, and all heavy items. This keeps the COG low. Remember... BRIDGE DECK CABINS SHOULD BE STREAMLINED AND RELATIVELY SMALL!

This stable, low COG, low windage, good visibility, minimally pounding platform, is combined with light weight, so that a small but easily reefed rig will drive her, EVEN hard to windward.

With skill, experience, and good judgment, she could easily take you around the world... with safety, speed, and relative comfort.

Many of the best "designs" are older ones, for the custom "one off" builder. (Back in the day when, IF you wanted a multihull, you built it)! It is how I got all three of mine...

These "better designs", were better because they were not designed to sell boats, they were designed to sell plans to build boats. The priorities of the experienced multihull home builder, were generally "wanting the more serious cruising type of vessel", for real world cruising. We didn't expect as much of an "apartment at sea".

IF you look carefully, there are still some great, still seaworthy examples of these craft out there. A few production cats qualify as well. Of all the characteristics that one must look for, they are ALL important, in just the right measure, but good wing clearance is #1. Pounding is not just noise. If it is bad enough, for long enough, it is the sound of your boat coming apart!

Good luck in your search!


P.S. This is a shot of the wing clearance of our Searunner 34 Tri., for example. Although we haven't, "yet", sisterships have circumnavigated safely. We have driven her HARD to windward, in 40+ knots of wind, and 13 to 15' waves, ALL day long, with minimal pounding or complaining.

The Cat, is also a "one off". It is the 34' long "Magic Carpet", and took our Australian friends, (a retired couple), around the world, over 10 totally safe years. They kept the overall cabin height, as well as windage, VERY low, AND wing clearance high, by living with just 5' head room in the small bridge deck cabin. HEADROOM can be sacrificed, but in just 34' LOA, the tall cabin, belly dragging alternative, is no longer a "round the world" boat. The same applies in larger boats as well, but they can have a bit more headroom and keep the same excellent proportions.

[webejammin]

Nice looking one off tri.

Has slap ever really damaged a catamaran ? Or is it just noise ?

[Dragon Lady]

I have read reports of boats being badly damaged, but as usual it would depend on many factors.
How does you Gemini go?
They look pretty low to me.

[Dulcesuenos]

I think there is a huge difference between slapping and Slamming. The smaller endeavor cats were slippers at anchor no biggie but in rough stuff slammers though no failures or damage from it. Kind of like a powerboat can take a beating and never have an issue. The older cats with wood coring if they had water intrusion into structural areas could start to show damage after a while. The gemini. I heard was more like slapping. Our new cat rarely does either. We covered 240 miles south from Port Canaveral to the keys and never pounded once into 15 + kt headwinds and storms.