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Old 02-11-2014, 22:25   #1
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The bow of cats

Why is it that the bows of cats are all vertical? I like the look of older monos and they had such beautiful lines but multis not so much. Now apparently aluminum cats seem perhaps even more so. Why is that? (Ps. I think the only real serious option for safety in a cruising boat is aluminum). Now you also take into account that many boats seem to be made in Europe (for their tastes) and I think it is very hard to find a nice looking cat.
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Old 02-11-2014, 23:07   #2
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Re: The bow of cats

Have a look at Wharram designed cats, they have pointy bows and sterns providing reserve bouyancy. JW is heavily inspired by the ancient Polynesian sailing cats (Va'a) that could be 70-80 ft long
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Old 03-11-2014, 00:12   #3
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Re: The bow of cats

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Originally Posted by justlearnin View Post
I think it is very hard to find a nice looking cat.
Well as they say, beauty is in the eye of the beholder. Its not my place to try to change your opinion, but merely to say, that a lot of people disagree with you.
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Old 03-11-2014, 01:18   #4
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Re: The bow of cats

Check out Derek Kelsall's designs.

He believes the tapered bow will slide over an obstacle and cause less damage in a collision. Netherless if you really wanted a vertical bow he would draw it.

Catamarans - Kelsall Catamarans - Boat Designs
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Old 03-11-2014, 02:09   #5
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Re: The bow of cats

Put simply, a vertical bow offers the most buoyancy for a given length, and the longest waterline. So it's an efficient shape. However many boats are designed with looks as a priority over practicalities.

I prefer vertical bows - I've always preferred content over style I guess.
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Old 03-11-2014, 05:36   #6
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Re: The bow of cats

Form follows funciton:

The pretty long overhangs you love so much in cruising boats are mostly an aberation brought about due to racing rules. It's well established that the longer the waterline of a boat the faster the boat. For a period, waterline length was measured with the boat sitting at the dock. Designers figured out that by putting in long overhangs, they could have a 30' boat rated as if it was a 22' boat. Then once the boat heeled over in a stiff breeze, the sides of the overhang would drop down into the water effectively increasing the waterline length and the speed. I believe most of the new rules have corrected this as there were some rather silly designs that were approaching dangerous in an attempt to push the rules.

That trick doesn't work with cats since they don't heel over, so there was never a reason to use it. You will also find the occasional mono marketed towards cruising with a plumb bow as it maximizes speed and internal space with less regard for racing rules.

Interestingly, you see some of the racing sillyness creep in with high performance cruising cats but it's the opposite. The bows actually have a reverse rake. It's an attempt to allow the bows to pierce the waves rather than ride up and over them as the vertical motion saps speed more so than punching thru the waves.
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Old 03-11-2014, 06:02   #7
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Re: The bow of cats

It isn't all about racing rules. I believe that overhangs in cruising boats make sense for several reasons. For one, in light air, with little heel angle, the wetted surface is less -- then, as you point out, valhalla360, as the wind picks up and the heel angle increases so does the waterline. Second, bow overhang helps with anchoring.

Of course there's the subjective aspect as well. To my eye, plumb bow and stern make the boat look like the box it came in
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Old 03-11-2014, 06:08   #8
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Re: The bow of cats

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It isn't all about racing rules.
True. There are some very good reasons for the overhang that you see in mono-hulls that has nothing at all to do with the rules. But then Valhalla did say "mostly," not "all."
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Old 03-11-2014, 06:32   #9
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Re: The bow of cats

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To my eye, plumb bow and stern make the boat look like the box it came in
Although I tend to agree with you, that is why they make different boats.
I never realized it, always thought I was more of a "modern" person, but I've come to the conclusion that I'm a traditionalist.
The modern America's cup boats are I'm sure that fastest things they are,
but I want to see the J class race some day, not the America's cup boats.
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Old 03-11-2014, 06:37   #10
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Re: The bow of cats

The advantage is that potentially a slim vertical bow will cut through the water as it buries, so the boat doesn't slow down, then potentially broach or pitchpole. A big flared-bow makes the pitchpole worse, not better, as the submerged hull is slower to return to the surface while the sails are still pushing forward.

Modern catamaran bow designs offer minimum resistance to the waves and are able to regain the surface with little effort.

Vertical bows keep the boat moving in big wind and waves.
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Old 03-11-2014, 06:37   #11
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Re: The bow of cats

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It isn't all about racing rules. I believe that overhangs in cruising boats make sense for several reasons. For one, in light air, with little heel angle, the wetted surface is less -- then, as you point out, valhalla360, as the wind picks up and the heel angle increases so does the waterline. Second, bow overhang helps with anchoring.

Of course there's the subjective aspect as well. To my eye, plumb bow and stern make the boat look like the box it came in
Yeah, a modest amount isn't neccessarily a bad thing but when you see a 30' boat with 4' overhangs on both ends, that isn't about being a good seaworthy boat or light air cruising. (plus on a cat, they don't have balast so they do pretty good in light air).

In a cruising boat, squeezing out that extra 1/10th of a knot upwind in light air, just isn't that important to most cruisers. When you can pick up 1/2 a knot running downwind in moderate winds on a typicall passage with a longer waterline length, that makes a much bigger difference.

You can make some arguements about not buryng the bow but you can make a seaworth boat with plumb bows.

I think a lot of them are the result of marketing to sailing purists who could care less what performs best. They want it pretty. By a similar token, I enjoy seeing an old model-T in a parade. Wouldn't want to own one as a primary vehicle though.
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Old 03-11-2014, 08:05   #12
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Re: The bow of cats

There are a couple of reasons for the vertical bows, which are magnified in multihulls compared to monohulls.

1) changes to the primary racing rules eliminated the advantage to long overhangs. So designers got rid of them. They were always silly from a design standpoint, but old measurement rules pretty much demanded them.

2) verticle bows increase waterline length at little extra build cost. So the boat can be made faster, have less hobby horsing, and don't cost much.

3) longer LWL increases speed, and allows boats to sail with less heel. So go faster, more comfortably.

4) for catamaranse this is doubly true since unlike mono's they can't heel over 20 degrees to increase the LWL. Their waterline shape is effectively static.

5) the "pushing things out of the way" argument is just silly. Unless you are in an ice breaker none of us intentionally hit things. And just because a boat doesn't have overhangs doesn't mean it has a deep bow. Most of the bow knuckles are kissing the surface, so if you hit something it just pushes the junk down.

Personally I don't like overhangs and where others see beauty I see lost oportunity. But truly it is in the eye of the beholder.
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Old 03-11-2014, 11:30   #13
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Re: The bow of cats

This discussion seems to be proceeding on the assumption that boats were designed with front overhang only for the purposes of aesthetics, or in an attempt to get around racing rules on monohulls by having an unmeasured increase in LWL when a boat heels. This assumption is false.

Naval architects have known for a couple of centuries that hull speed in a non-planing hull (the only hulls that existed 200 years ago) increased in proportion to the length of the waterline. The clipper ships and other sailing vessels of the past were designed with that in mind - i.e.. a particular waterline length was chosen, but then front overhang was added. Was this purely for reasons of aesthetics? Were those commissioning large clipper ships (or those commissioning smaller fishing schooners such as the Bluenose) prepared to pay more more for an aesthetically pleasing overhang that added cost and worsened the performance of the vessel by adding weight and decereasing stability? Of course not. Were they designed with front overhang to take advantage of a rating rule? No, as there were no rating rules.

IMO, one should think of a boat as being designed to a specific waterline with the subsequent consideration being whether the builder (or customer) wishes to pay a little more for front overhang. There are several advantages:

1. Front overhang increases the area of the foredeck, assuming the coachouse and all other aspects of design remain the same. This facilitates sail and anchor handling, etc., on a monohull or trimaran. It also permits a symetrical spinnaker to be flown further forward off the bows of a catamaran. This benefits self steering effect downwind.

2. Forward overhangs also reduce spray on the foredecks of both monohulls and multihulls. This is important if one has to go forward when underway.

3. Foreward overhangs provide additional bouyancy forward on the same waterline length - in extremis, the volume increases on three rather than two planes as the bow is depressed. This reduces the risk of burying a bow - a very dangerous phenomenon for both monohulls and multihulls that can lead to a pitchpole or capsize. One of the earlier posts suggested that it would be harder for a submerged bow to resurface if there was a front overhang; no doubt true as the bow would be longer. However, the key is in avoiding burying a bow in the first place, where added front overhang has a distinct advantage.

4. On monohulls or trimarans (or catamarans such as mine, with bow rollers off each bow), front overhang reduces the tendancy of the anchor banging into and damaging the topsides of the boat as it is being hoisted back aboard.

As naval architect Robert Perry wrote in Sailors' Secrets - Advice from the Masters, Michael Badham and Robby Robinson, International Marine, Camden, 1999 at p. 193:

"Some things, though, begin to look better the heavier the weather gets. Plumb stems are a modern trend. The obviously can maximize waterline length, but in a cruising boat do you want to give up a foredeck and make your boat into a submarine....? Traditional elements like overhang are traditional because they work."

While the advantages are less compelling in a cat than a monohull or a trimaran, nevertheless there are still some valid reasons for specifying a bow with some overhang on any boat.

Brad
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Old 03-11-2014, 11:34   #14
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Re: The bow of cats

obviously os, bristol channel pilot cutters are new designs then !!
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Old 03-11-2014, 11:51   #15
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Re: The bow of cats

The trend isn't plumb bows, but reverse bows...

Which at least avoid the boxy LOOK.



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