Whats the reason for the huge differences in displacements in similar sized boats? - Page 4 - SailNet Community
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post #31 of 39 Old 08-28-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

David,

I could possibly see some of Rich's points using the European boat rating, ie A is ocean, B is semi protected, C is lake use. While not an engineer, I have not seen that type of wording in the specs per say. Ocean A does have a spec a boat will handle IIRC a 10'ish meter wave vs 8 meters for the B, and do not remember the C off the top of my head.

A also have room for a life raft among other things B and C rated boats do not have.

I will admit, this is a swag as to where he might have those specs.

Marty

edit,

European rating rules
now that I am rereading, it does look like a typical law/rule, more mumbo jumbo than anything!

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post #32 of 39 Old 08-28-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

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Originally Posted by bobperry View Post
Could we try some wine in those glasses instead of gravel?
I tried this experiment with wine last night and got very confused, frustrated and spilled some wine. Then I had a brilliant idea. I drank the wine and did some work on my boat. I felt positively buoyant!
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post #33 of 39 Old 08-28-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

This is thin ice.

Unless you are designing a high tech, around the buoys racer you should expect any boat to be able to take any punishment, within reason. You can never anticipate when the owner of an Islander 26 is going to try to sail from Newport Beach to Hawaii. So the boat better be up to the challenge. With reasonable modifications to insure offsure safety. But these mods should not include basic structure.

Good old Puget Sound can be very hard on a boat. We get a square chop that can pound some boats to pieces. You can be 300 yards off the beach and in terminal conditions.

Alaska:
Did you actually drink the wine or did you " displace" it?
I'll go on record as saying this was a displacement thing and you really did not drink much wine.
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Last edited by bobperry; 08-28-2012 at 02:25 PM.
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post #34 of 39 Old 08-28-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

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Alaska:
Did you actually drink the wine or did you " displace" it?
I'll go on record as saying this was a displacement thing and you really did not drink much wine.
May I reference you next time I "displace" too much wine and get that sinking feeling?
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post #35 of 39 Old 08-28-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

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Originally Posted by bobperry View Post
This is thin ice.

Unless you are designing a high tech, around the buoys racer you should expect any boat to be able to take any punishment, within reason. You can never anticipate when the owner of an Islander 26 is going to try to sail from Newport Beach to Hawaii. So the boat better be up to the challenge. With reasonable modifications to insure offsure safety. But these mods should not include basic structure.
What would be the kind of mods you have in mind that you would consider reasonable?
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post #36 of 39 Old 08-28-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

Alaska:
Sure, You can blame me.

David:
That could be a big list but I'd start with a good companionway and a bridge deck if I wanted a conservative approach. The rest would be pretty much standard fare for going offshore, i.e. jacklines, wind vane etc.

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Re: Whats the reason for the huge differences in displacements in similar sized boats

ah yes, the good old puget sound square chop! The worst place I have found is around point no point and the scatchet head area. Long fetch, if a gale type southerly and a BIG flood ie one of our 14' monsters, then life gets really bad out that way, 4'up 4' wave to wave crest! oh boy! reminds me of foulweather bluff 3 & 4 yrs ago, both yrs had winds in the upper 30's to low 40's with a flood! hope it is like that in a month or so, my boat does better in that than flat calm and low winds......or maybe the driver/crew do better when not standing still, and drinking too much alaska beer! or bc beer or beer in general...........

Marty

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Re: Whats the reason for the huge differences in displacements in similar sized boats

Ignoring the Archimedes, I'm going to have to say that Jeff's answer both confused and illuminated the subject for me.

Lets compare a Pacific Seacraft 34, and a Catalina 34.

The Catalina has a wider beam, longer LWL and 200lbs more ballast. According to my original theory the Catalina should displace more then the Pacific Seacraft, yet it displaces 1550lbs less.

After reading Jeff's post this would seem to indicate that the Catalina is a better designed boat? To me these numbers seem to say that the Pacific is a more robust boat because the higher weight, at least to me, means a thicker hull which would be a good thing, wouldn't it? Or is this weight just adding unnecessary stress to the boat?
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Re: Whats the reason for the huge differences in displacements in similar sized boats

The C34 will be a faster, possibly stiffer boat than the PSC 34. One the ballast disp is almost 10% more, ie 35% vs 45 for that Cat. Disp to the length is lower for the Cat, Sa to disp is around 15-1 for the PSC, and close to 17-1 for the Cat. These last figures in car speak, would be HP/lb of car wt! Hence why from a phrf rating standpoint, the catalina is around 150, the PSC 195. As a comparison, here is a link to my boat, which depending upon the where it is sailed, phrf ranges from 165 to 192. Using the link I found the above ratings for the PSC and Cat, it is 159. So dang near on par with the cat, but I am 6' shorter, and half the wt of the psc!

I will admit, the scantlings, ie build of the psc is heavier, potentially stronger than a catalina, or my Jeanneau for that matter. BUT< all three have crossed oceans!

Marty

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