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  #3361  
Old 01-26-2014
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by PCP View Post
Why do you say this? It is true that stability curve makes no sense but a value of about 130º or even superior for an AVS is pretty good, the hull design has nothing new or interesting but it seems adequate to me and the boats are heavy contributing for the overall stability. Besides they sailed extensively offshore with a good proven record regarding seaworthiness.

So, why do you find them dangerously unstable?

Regards

Paulo
Good to see some feedback I guess I should have said could be dangerously unstable.
Tad's estimate for 130 degrees was without the cruising load and added equipment that tends to accumulate on a boat and that reduces stability considerably more than the half tanked minimal hull consideration, he had mentioned that to Brent before. It could reduce the limit of positive stability easily by 30 degrees. An inclining test on a cruising boat with all gear extant and in position is the real test. It's one you'd expect Brent would really want to know about having mislead so many of his clients for so many years telling them the design is stable to almost the full 180 degrees.

I've done a lot of stability studies on sailboats and the inclining test is often a real eye opener for the owner. The published stability curve from production boats is an ideal and they may not even make allowance for the gear the boat is actually sold with, let alone the owners additional cruising gear. Some designers work up all sorts of extras in their weights study some just treat it like a bare boned racing boat.

ISO STIX labelling is becoming something of a standard requirement but what you think of STIX is another matter and many designers aren't happy that it accurately reflects the seaworthiness of a sailboat.

The longer a boat the bigger the sea it can cope with, with a lower risk of being inverted, and the stability can be reduced accordingly. Considering Brent has common designs for 27 to 36 feet and more recently a 40 footer and he promotes them for high latitude offshore sailing then stability is the real key to safety.

Here's a good illustration of the 98 Hobart fleets inversions and their length relative to limit of positive stability superimposed on the UK requirements for sailing boats carrying public.
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Last edited by MikeJohns; 01-26-2014 at 02:03 AM. Reason: comma
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  #3362  
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Re: Pros and cons of steel sailboats

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Originally Posted by MikeJohns View Post
Good to see some feedback I guess I should have said could be dangerously unstable.
Tad's estimate for 130 degrees was without the cruising load and added equipment that tends to accumulate on a boat and that reduces stability considerably more than the half tanked minimal hull consideration, he had mentioned that to Brent before. It could reduce the limit of positive stability easily by 30 degrees. An inclining test on a cruising boat with all gear extant and in position is the real test. It's one you'd expect Brent would really want to know about having mislead so many of his clients for so many years telling them the design is stable to almost the full 180 degrees.

I've done a lot of stability studies on sailboats and the inclining test is often a real eye opener for the owner. The published stability curve from production boats is an ideal and they may not even make allowance for the gear the boat is actually sold with, let alone the owners additional cruising gear. Some designers work up all sorts of extras in their weights study some just treat it like a bare boned racing boat.

ISO STIX labelling is becoming something of a standard requirement but what you think of STIX is another matter and many designers aren't happy that it accurately reflects the seaworthiness of a sailboat.

The longer a boat the bigger the sea it can cope with, with a lower risk of being inverted, and the stability can be reduced accordingly. Considering Brent has common designs for 27 to 36 feet and more recently a 40 footer and he promotes them for high latitude offshore sailing then stability is the real key to safety.

Here's a good illustration of the 98 Hobart fleets inversions and their length relative to limit of positive stability superimposed on the UK requirements for sailing boats carrying public.
Yes I agree that any 36 ft boat is a bad idea for high latitude and I agree that misleading information is plain wrong but then regarding 36ft boats the ones from Brent seem better to me regarding stability then the common mass market offers, they have at least a similar AVS and the superior mass of Brent's boat will give it a superior stability. what you say regarding storage and equipment is as true to Brent's boats as to any other boat.

Yes I agree that STIX as a measure of a boat seaworthiness makes no sense mostly because it gives a big negative importance to a boats sail area, as if a sail could not be easily reefed or taken out. I really don't understand that criteria that is responsible to a lot of distortions regarding STIX.

A performance boat with a huge stability running in stormy conditions with storm sails is a lot safer than a typical cruising boat with a considerable smaller stability sailing on the same conditions. In most cases the cruising boat because it can carry much less sail (because it has less stability), on account of that smaller sail area has a better STIX (assuming identical AVS).

Regards

Paulo
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  #3363  
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Re: Pros and cons of steel sailboats

I am amazed. After mire than ten years and being ridiculed on the BD forum to the point that he changed his name to "Jack Hickson"? in order to defend himself only to get even more ridicule as Jack Hickson he still clings to the idea that his 36'er has a LPS of 165 degrees?

Keep in mind this claim comes from a guy who doesn't understand the use of an inclining test in a stability study. Very curious for someone claiming to be a yacht designer. I'll let this photo do my claiming for me.


Also this is a guy who in a discussion over Wolfenzee's boat claimed the LPS for Wolf's boat could be as high as 182 degrees! I literally chuckled for days after that.

In claiming a LPS of 165 degs for his 36'er BS just proves he knows nothing about stability. As usual he had picked up little fragments of naval architecture and then tried to glue them into a picture he likes. But the way he glues the pieces reminds me of that scene in GOONIES when the kids break the mother's statue of David and glue it back together with David's dick upside down. As reconstructed by BS/Jack Hickson the finished picture makes no sense. Having been involved with sailing vessels as long as he has I can't understand how BS can be so confused over the math and mechanics of stability. This is a subject I tackled when I was a kid. I knew it would be critical to my work. Just a quick look at stability studies of other, similar proportioned boats should be enough to teach BS that his whole approach must be fundamentally flawed.

On the other hand, it's been flawed for over ten years so I now must think that Brent is incapable of learning the basics of stability. He still doesn't get it. Buying a set of plans from a guy who doesn't understand stability must be comforting. No?

Yow!
I just went back and read more of the posts from that 2008 BD forum. Those guys are pretty hard on old Jack Hickson aka BS aka Brent.

"Your boats are extremely ugly and an insult to steel boats in general - geez, that ugly slit and corner at the bottom:eek"

I don't think I have been quite that direct.
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Last edited by bobperry; 01-26-2014 at 10:48 AM.
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  #3364  
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Re: Pros and cons of steel sailboats

Still its too bad in a way the concept of bilge keels hasn't been more aggressively pursued in recent years. To my simple understanding if you had twin bulbed keels you might get very reasonable stability without major draft and ability to careen while being upright in a large tidal zone much like the British do.
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  #3365  
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Re: Pros and cons of steel sailboats

Out:
We need Paulo on this. He has posted several new European models that have modern fin and bulb tandem keels. They look quite good. But there is little to gain from having two crude, low aspect ratio BS keels other than the ability to have the boat stand on it's "feet" when the tide goes out.
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  #3366  
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by bobperry View Post
Out:
We need Paulo on this. He has posted several new European models that have modern fin and bulb tandem keels. They look quite good. But there is little to gain from having two crude, low aspect ratio BS keels other than the ability to have the boat stand on it's "feet" when the tide goes out.
Nice of you to say that even if I believe you know more than enough about it.

Some interesting information even if not necessarily not biased:

http://andycunninghammarine.co.uk/do...nTwinKeels.pdf

Bray Yacht Design and Research Ltd. - The Advantages of Twin Keels

Of course you know quite well that in what regards efficiency nothing beats draft and an elongated torpedo keel but in what regards the need of low draft a twin keel can be an overall better solution than a wing keel. Sure it can be designed a very efficient wing keel but an efficient one will be fragile due to needed small profile of the wings that are on the lower part of the keel.

A twin keel is not fragile and can take the weight of the boat allowing it to stand for drying up and that has many advantages, not only in remote places for repairs but also in tidal waters or even to have the boat stored in land.

Like the wing keels, a good performance twin keel has to be profiled and hydro-dynamically studied for having a low drag but contrary to the wings of a wing keel that means not necessarily a weak one since in most cases those keels are a single steel structure.

They also have advantages in what regards roll and sea motion comfort. I believe that on those two links are covered most of the advantages.

I posted also about them on interesting sailboat thread namely a comparison performance on the same boat with each type of keel by Marc Lombard.

Interesting Sailboats

Interesting Sailboats

Regards

Paulo
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Last edited by PCP; 01-26-2014 at 11:36 AM.
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Re: Pros and cons of steel sailboats

Thank you Paulo- Very interesting reads. Particularly like the concept of having asymmetrically chords to the keels. I have no experience of twin keeled boat let alone those with modern appendages. Just wonder if with the narrow chord of the fin and the greater lateral plane of the bulb is there a difficulty when these boats are subjected to unintentional groundings. Do they act as anchors if the bulb extends forward of the fin?Is that why the bulbs only extend aft? Too wit, are you forced to free the boat by going directly backwards with no other choices and then in trouble if the bulb digs in? I would think there is no issue if you can wait out the tide and float off ( presuming there is a sufficient tide). I would think twin keels would make it difficult to pivot off and be subject to damage to the high aspect portion of the fin being placed in torsion if of modern design. Is this thinking wrong?
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Re: Pros and cons of steel sailboats

I think for a cruiser the T keels are more problematic than the bulbs 'aft only' mainly in that a T keel will never shed kelp or other flotsam that might get snagged by accident.

I can see a big advantage in general with the modern twin keels that are built to be able to dry out.. paint/repair anywhere with a tide, if you're not on a schedule you'd have access to coves no one else is likely to get to.. The RMs tick quite a few boxes for me..
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Re: Pros and cons of steel sailboats

Out:
Are you sure about asym foils? It's not like you can retract one keel. I'd think the fins would need to be symetrical.

Keeping the bulb aft of the leading edge just means less trouble catching kelp. On the Sliver project I preferred a T keel but the client did not want a kelp cutter so we went with the L config form the bulb.

I think you make a good point about ground and getting off by pivoting. Around here as soon as you ground the first thing to do is to heel the boat over to reduce draft. That would be a problem with tandem keels.

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Last edited by bobperry; 01-26-2014 at 12:34 PM.
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Re: Pros and cons of steel sailboats

Same here. Either back wind the sails or put a kedge off the spin halyard with line going straight abeam. Given Weight Watchers hasn't taken hold yet sometimes my fat butt out on the pole will work. Don't see how you would do that with bilge keels. So far only hit sand and still counting times on one hand after 30+ years. Still, hate that when it happens. Makes you humble.
Maybe I miss understood Andy's article.
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