Most of the monohull sailors that I know who have sailed cats, complain
that the combined bow waves meet under the bridge deck creating a very
uncomfortable pounding. This effect is said to worsen as wave height
increases. It would seem that the higher off the water the bridge deck
the less this would be of concern but there are obvious limits to this
approach.

My question- Is this an issue with tri's I would also be interested
in input from cat sailors as to how much this is an issue with their
boat and is the only solution increased height for the bridge deck?

thanks sk

wrote:
Most of the monohull sailors that I know who have sailed cats, complain
that the combined bow waves meet under the bridge deck creating a very
uncomfortable pounding.

Certainly, if you've never heard/felt the pounding, it would be
disconcerting and perhaps uncomfortable at first. I have to admit
that the first time my PDQ 36 cat surfed down a wave at 12 knots and
pounded when it hit bottom, I dove for the bilges to see just how fast
we were sinking! I learned quickly that pounding has a lot to do with
the angle at which you hit the waves. If you power a cat straight
into a chop, you will certainly pound, although I found my old Nonsuch
pounded worse in this situation (though perhaps not as loudly). When
we want to power upwind against a nasty chop, I'll set the main very
flat, pulled to weather, and powersail about 30 degrees off the true
wind; this almost completely eliminates the nasty pounding. One huge
advantage the cat has in this case is that we can maintain 5+ knots
powering against a 25-30 knot breeze with chop, while most monohulls
will turn back.

On normal points of sail, we have relatively little pounding in seas
under 4-5 feet. It doesn't really affect the boat's motion, its more
of a sound thing, with a little rap. Far more annoying are beam seas,
which can suddenly raise one hull while lowering the other. This can
be quite disconcerting because the cat is normally completely level,
and then suddenly lurches 10-15 degrees. However, this is easily
controlled by the helmsman, since angling the boat just a few degrees
to the seas (or wake) totally eliminates the problem. In fact, on the
ICW, I always waved the powerboats through, telling them not to reduce
speed for me since I should be able to handle it with no problem.

The beam seas problem is such an issue that in certain conditions the
autopilot cannot be used, since a firm hand, and anticipation, is
required to keep the boat on an "even keel." In this situation I find
that I have to stay on the helm for the duration, since my wife cannot
maintain the necessary focus for extended periods. I would not expect
the average monohull skipper to have this skill, and I often wonder if
this motion is what first time cat sailors refer to as "pounding."


This effect is said to worsen as wave height
increases.

Well, it doesn't happen much in flat seas! But the design of a cat
normally dampens waves so you can't say that a boat with 1.5 foot
clearance will pound in 2 foot seas. I usually don't give it much
thought until I hear "4-6 feet chop."

It would seem that the higher off the water the bridge deck
the less this would be of concern but there are obvious limits to this
approach.

The Victory Cats are designed with a high clearance - in fact by a
former PDQ owner who apparently wanted to reduce pounding. Our final
decision to go with PDQ was at a show where a Victory was next to the
PDQ and we found the "high design" rather off-putting. In particular,
the high freeboard makes the Victory rather inaccessible from the
side. I might imagine this is better for long offshore passages, but
is it worth the windage?

This issue largely goes away with modern larger cats, over 40 feet,
such as the Manta and the PDQ 44. They have been "scaled up" with more
clearance (and high freeboard), plus the larger beam reduces the beam
seas problem.

Another point - older designs, with solid foredecks instead of tramps,
tend to hobby-horse a lot more then newer cats. (And in some cases I
mean a *lot* more, as in a sailing pogo stick!) Add this to low
clearance and overloading, and you could have a boat that would pound
in even a modest chop. For this reason, I didn't consider older,
smaller cats, under about 32 feet.



My question- Is this an issue with tri's

Its a moot question, since there are virtually no cruising trimarans
being built. The light folding tris (F-27 and the like) have mesh
"decks" and thin hulls so there is very little to pound.

The folding tris and cruising cats are such totally different design
points that if you're deciding between them you should get more real
experience before buying either!

I would also be interested
in input from cat sailors as to how much this is an issue with their
boat and is the only solution increased height for the bridge deck?

If your intended use is coastal cruising, I wouldn't worry too much
about it. However, you should definitely get some time on any design
you intend to purchase. Just like there are major differences in
monohulls, there are differences in cats.

Jeff,
thanks for the input. There are a few large tris for sale there is
one in BVI that is 63 feet which at least by my standards is a pretty
large chunk of fiberglass.

I have every intention of following your advice and renting/chartering
everything I can find to establish what is the perfect boat for me.
Which actually brings me to another question that I have posted
elsewhere. How would one go about finding a charter that would take
one out in relatively serious weather. I figure that most bosts will
behave themselves in the perfect weather but I would like to be assured
that when things get a little rough I will not be fighting the boat as
well as the weather.

thx sk

wrote:
Most of the monohull sailors that I know who have sailed cats, complain
that the combined bow waves meet under the bridge deck creating a very
uncomfortable pounding. This effect is said to worsen as wave height
increases. It would seem that the higher off the water the bridge deck
the less this would be of concern but there are obvious limits to this
approach.

My question- Is this an issue with tri's I would also be interested
in input from cat sailors as to how much this is an issue with their
boat and is the only solution increased height for the bridge deck?

thanks sk


I've got a 40' cat with bridgedeck clearance of about 2' (depending on
the load). In sheltered waters around here the biggest waves I've
seen are about 4-5' (heading into them beating). Only ever slapped
the bottom very lightly a few times. Friends with a cat with less
clearance said that big waves jarred their fillings. After some
modifications, the clearance will be about 2'3" when fullly loaded.

The usual rule of thumb is 0.05 LWL is about enough clearance on a cat
for offshore sailing. More is of course better! There will always be
conditions that will cause a particular cat to slap/slam, but you're
trying to minimize that by having enough clearance. Geminis, PDQ 36s,
most South African cats in Caribbean charter service do not have
enough clearance (Moorings/Leopard). Maybe they were sailing these?
The French cats generally do have enough clearance.


I would take the motion of my boat beating to windward in moderate
seas over any comparable size monohull. My daughter can stack
dominoes on their short edge about 4 high before sea motions cause
them to collapse.... We *once* spilled a glass of orange juice in a
bad wave and was cause for great excitement. You get the idea.

Regarding tris, the smaller folding type Farrier tris have issues with
the lower folding struts hitting waves, but this only produces spray,
not slamming. Older Piver/Searunners with solid wings sometimes have
this trouble when heavily loaded, but I have less direct and anecdotal
information about them.

Evan Gatehouse

We are starting the building process for Levitation... She is a 50' X
26' trawler power cat... The bridge clearance is 3 feet at full load..
Part of the design process was looking at issues such as stability and
pounding... The solution (we believe) is adequate bridge clearance,
keeping the ends of the hulls uncovered by the bridge, and more beam
than the popular factory designs..
The advantage of having 3 feet of bridge clearance at full load is
intuitive and no deep analysis is needed... The increased dock height
is handled by either med mooring or by opening the boarding gate on the
dock side and using a dock step....
More beam gives you two things immediately...
The first is the increased hull separation dramatically dampens the
inner bow waves from ramming each other and slapping up against the
bridge... The second is that stability is increased significantly if
caught beam on by a rogue wave...
The final part of the equation is that there is unburdened hull both
fore and aft - with generous bulworks... Commercial cat designs inflate
the bridgedeck until it covers every foot of hull and what you are left
with is a pontoon boat with a condo on top... What I did was design a
35 foot bridgedeck cat and put it on 50 foot hulls... The ends of the
hulls are not covered by deck, can plunge into the wave just like a
monohull, until the increased flotation lifts the bow (stern) and there
is no horizontal surface near the hull ends for the exploding wave to
slap against.. ..

Most commercial boat designs are aimed at looking good at the dock, and
everything else is secondary... Ya gotta march to a different drummer
if you think for yourself..

denny

wrote:
Most of the monohull sailors that I know who have sailed cats,
complain that the combined bow waves meet under the bridge deck
creating a very uncomfortable pounding. This effect is said to
worsen as wave height increases. It would seem that the higher off
the water the bridge deck the less this would be of concern but there
are obvious limits to this approach.

My question- Is this an issue with tri's I would also be interested
in input from cat sailors as to how much this is an issue with their
boat and is the only solution increased height for the bridge deck?

Not an issue with most tri's as other posters have already pointed out. You
might find the unusual action of a tri across a quartering sea to windward a
bit disconcerting at first, the action can be a bit unusual. That sensation
is the only thing that has ever made my wife queasy at sea, which surprised
us both, and we didn't discover until after buying the boat.

Most Tri's sail more like mono's than cats, owing to the common central
hull. The differences are beam on to choppy seas on the tri can lead to some
slapping water on the floats, and occasionally a greenie over the cockpit
forced up between hull and float. On our 10m Farrier a short bay chop of
around 4 feet is the worst and most frustrating if needing to be taken on
the for'd quarters to the beam. Irritating and wetting, but nothing more.
Out in the Ocean swells, no problems at all.

I prefer tri's for sailing myself, but I'm not at all a fan of solid wing
tri's, which can slam going to weather, especially if overloaded, and can be
subject to massive stress loads to the beams by breaking waves. Of course,
no tri I've seen competes with a modern bridgedeck cat for luxury at anchor.

Ian

Anything pushed upwind at over 8 knots into a gale will pound. Them's
the rules. I'm just recovering from a brute of a trip from New Zealand
to Hawaii non-stop on my 42' cat-- no problem usually, but with bad wx
luck it can suck. We don't usually pound noticeably with 3' clearance
and a short bridge deck, but this time there were some moments when I
thought the table was going to impact with the overhead... I'm feeling
more okay with this now that a good deal of rum has been applied.
Anyway, I have some friends who have a 36' Newick tri and they report
pounding on the wings in some conditions. This can be a problem for
them as their head is a whole in the wing deck and a very good butt to
deck seal is required in these conditions... I sure do love the way
that boat sails, but I don't think my colon would be up to that kind of
punishment for long...

-- Tom.