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CherylannJohn 07-15-2004 03:54 PM

Motion at Sea
 
Take two boats of about 38 feet and 18,000 lbs.

One has a modern "fairly flat" underbody with a fin keel and spade rudder.

The other has a older, more of a "Vee" shaped underbody with a modified fin and skeg hung rudder.

Will the different shapes alone change the motion at sea? If so, which one gives the best ride?


John

Silmaril 07-15-2004 06:55 PM

Motion at Sea
 
There are so many other factors that affect the "Ride" of a boat it is impossible to give a blanket statement from your limited information. If you had two particular boats in mind, there would be more to go on.

That, and what is a comfortable "Ride" to some, may be unacceptable to others.

Jeff_H 07-15-2004 07:17 PM

Motion at Sea
 
There really is not enough to tell from your description except that 18,000 lbs is pretty heavy for a 28 footer so you would expect both to be a little rolly because they would have comparatively deep canoe bodies.

There are a lot of factors that control the motion comfort of a boat. The main factors controling motion comfort would include weight distribution, buoyancy distribution, and dampening. Your description touches on buoyancy distribution, but does not address the other factors at all.

There is also a difference in how people perceive motion comfort. Individuals have different thresholds for discomfort and the triggers of discomfort are purely individual as well. In other words, some people are bothered by the speed of the motion more than amount of the motion and other people are affected more by the amount of motion than speed of motion. And still others are equally affected by both. On that basis a boat that rolls through wide angles slowly is no more universally comfortable than a boat that snap rolls through small angles.

You have really asked a short question that would have a very long answer to fully address.

Respectfully,
Jeff

mmccoy 07-16-2004 03:16 AM

Motion at Sea
 
I''m no designer/architect but in my experience *in general* (and all other things being equal) the flatter bottom boat will be more uncomfortable. The deeper ''V'' hull will cut thru the water better where the flat bottom boat will tend to ride on top and pound more in a chop.

But as the others have said there are a lot of other factors to consider (even beyond the boat itself). There are conditions where the flatter bottom boat would be more comfortable than the deeper hull. So take my VERY generalized statement with a grain of salt.

CherylannJohn 07-17-2004 02:28 PM

Motion at Sea
 


How much ride do I give up to have a turn of speed and be able to point? If you have to have two particular boats to compare try a Pacific Seacraft 37 and a Tartan 3700 as an example.

In addition, what difference does that wide stern on the 3700 do to performance?

Thanks,

John

Jeff_H 07-18-2004 06:24 PM

Motion at Sea
 
Given the two boats the Tartan 3700 should have a more comfortable motion and also be quite a bit faster. There are a number of factors that control motion comfort and a boat like the Tartan does well on most counts compared to the Pacific Seacraft.

The Tartan 3700 should have a substantially lower center of gravity and higher center of buoyancy. The Tartan should have a greater roll moment of inertia meaning a slower roll and since the roll axis is higher, should roll through a smaller arc as well. The Tartan''s deeper keel, and its keel and rig configuration should result in better dampening. Similarly the Tartan''s longer waterline should provide better dampening and mean less pitching as well. The Tartan''s finer bow should mean gentler impacts in a chop and a greatly reduced tendancy to hobby horse.

In other words the Tartan should have a substantially more comfortable motion.

As to speed, the Tartan should also substantially faster on all points of sail and in all conditions. The wider stern on the Tartan should give it more reserve stability (at the price of ultimate stability). The more efficient rig, and keel plus substanially higher stability should allow the Tartan to really exceed against the Pacific Seacraft upwind and because of its powerful stern, straight run, finer bow, and futher aft center of buoyancy the Tartan should walk away when reaching in moderate to high wind situations. The wider stern should permit the Tartan to surf better in a following sea and the finer bow and longer waterline should allow the Tartan to have better tracking than the Pacific Seacraft (except in extremely gusty conditions when the powerful stern sections on the Tartan would tend to generate a transient weather helm condition. In those conditions a helmsperson, an autopilot or a vane on the Tartan would need to steer more than on the Pacific Seacraft. I would expect this to be greatly offset by the lower helm loads on the Tartan.)

All of that said, these are two extremely different boats in terms of purpose, ease of handling, and accomodations. These are such extremely different boats that I cannot imagine a circumstance where a knowledgeable sailor would actually be making a decision between these two particular boats.

Respectfully,
Jeff

CherylannJohn 07-19-2004 05:17 AM

Motion at Sea
 
So it seems the answer to my question about whether the underbody affects the motion at sea is that its only one part of the equation...

The Tartan 3700 and the Pacific Seacraft 37 are different boats but similar in size and price. Having been on the Pacific Seacraft first with the broker, and also Nigel Calder in his book, telling us that this is THE boat I was duly impressed. Then going aboard the Tartan 3700 and talking to a factory rep. at the boatshow I had second thoughts.

The purpose is to go cruising in a boat that won''t make me sorry I chose it because of a unfound bais on my part before I became a knowledgeable sailor. I hope to get the help and some of the knowledge needed by asking questions of those that know something instead of those that have something to sell me.

Thanks,

John

Jeff_H 07-19-2004 06:01 AM

Motion at Sea
 
Hello John,

You are looking at two very expensive, purpose-built boats. Neither of these are good boats to own as a first boat, or as a vessel upon which to learn to sail (although the Tartan would be by far the better choice if you had to chose one of these to learn to sail on).

My best advice is to start with a relatively inexpensive, responsive 22 to 28 foot, used, fin keel/spade rudder sloop. A boat like that will allow you to learn the basics quickly and help you develop an understanding of your needs and tastes in a boat. You may only own that boat for a year or two but it will greatly shorten the learning process and in the end will save you a lot of money buying or damaging the boat that you will ultimately own.

I also want to point out that there are a whole range of really wonderful boats in your size and price range. Both of these are good boats for their specific purposes, but that their purpose may not be your own and there may be, and probably are, better boats out there to suit your needs and sailing venue.

Respectfully,
Jeff


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