Minimum Draft for Blue Water?

[Sabbatical II]

If safety and stability are the concern, then there is more to consider than simply draft as has been said before. You could have two identical boats, one with lead ballast and one with the same amount (in weight) of cast iron ballast and because the lead is denser the weight is concentrated lower, thus giving more stability.

The other thing I considered when choosing my current boat (in build) was how much all the stuff I take would effect stability. E.g. In a 42' boat I have 1100 litres water tankage (no watermaker). If it was a lightweight production boat, you'd be trying to get that all in under the saloon seats which are probably above the waterline level and thus adversely effecting stability. I have been able to have that tankage built in below the water line into the structural floors and I'm hoping full tanks increases the stiffness of the boat.

My boat has been designed to be a long haul cruising boat and the assumption is that we all bring too much stuff and this will effect certain designs more than others.

Greg

[Adelie]

Originally Posted by KJB

Example: Boat A and B are the same model, but boat A has a draft that is longer than boat B. Do both handle the open ocean equally well? I have come across this in my searches.

Any ideas?

Lets assume that A is the standard model and
B is the shoal draft version.

Further assume that B has increased ballast to compensate for the decreased draft giving approximately the same stability curve and point of vanishing stability. Lets say ballast is increased 10% and center of mass is raised 5% towards metacenter. As a guess roll moment of inertia will be slightly increased so resistance to capsize due to wave action will be also be slightly increased. This is all to the good in open ocean.

On the other hand the standard draft model will have a slight advantage sailing hard on the wind. This will be an advantage if your destination is upwind, you will be able to carry marginally less provisions, so the boat is marginally less loaded experiences marginally less fatigue and is marginally less likely to have a rigging failure.

Then again you will not be spending most of your time in the open ocean, probably less than 20% of your time will be on passage. Unless you are intending to go around non-stop or some other absurdity with your family.

So the ability to claw off a lee shore in heavy wind and waves starts to look a little more important given that you will spent a fair amount of time in thin water.

On the other hand the shoal draft version with new sails in good shape would probably do as well or slightly better upwind than the standard boat with older sails.

In a completely rational world a shoal draft boat would be less likely to run aground. This is not that world. Charlie Wing in "the Liveaboard Report" indicates that there was an inverse relationship between draft and the number of times a boat had been aground. My sense is that in mild or settled conditions when consequences wouldn't be as severe skippers of shoal draft boats got a little complacent about water depth either sailing or anchoring. My sense is that in heavy winds or in areas where the bottom is rockier rationality takes firmer hold and the shoal draft boat is less likely to run aground. My conclusions extrapolated from what Wing wrote.

My reccommendation is that a 40' or so boat with 5'-7.5' of draft is pretty reasonable. More than that I start to think it is a former racing boat that may have a lot of characteristics that would be fine racing but problematical cruising. That length boat with under 5' of draft I ask why? If it has a full keel or a centerboard then that about covers it. As an example the Bermuda 40 is almost 41' and draws 4.5'ish board up and it was designed for the Newport-Bermuda race which crosses the Gulf stream which can be very nasty during a blow. I think most people would agree that the Bermuda 40 is an acceptable blue water boat.

My feeling is that the moderate draft I mentioned above is a good compromise between upwind performance and general anchoring friendliness. If you were going to the Bahamas or were going to cruise the canals of Europe, then shoal draft would look more attractive.

As I use the terms capsize means the boat rolls over approximately upside down, knock down means mast in the water or just below, and founder means to sink, all distinct meanings.

For sailboats a capsize generally requires wave action to roll the boat over, exceptions would be the aforementioned J24 with a very limited range of stability or a vessel that is grossly overloaded or has it's stability compromised. An example of the second two is the recent capsize of a MacGregor 26 in San Diego under mild conditions, the boat was overloaded though not grossly so and apparently had not taken on the required water ballast which is believed to have seriously compromised it's stability.

[estarzinger]

Originally Posted by KJB

There is one thing I keep thinking on though; If a shoal draft is just as sea-worthy as a deep-draft (as some have supposed), then why make one?

the answer to that is pretty clear - the deeper boat will be faster, because (1) it can be lighter (less ballast) for the same righting moment, and (2) it will have less leeway going upwind.

By the way, properly made fin keels can be very strong and robust.

[gbanker]

4' of draft seems to work fine for our catamaran.

Seriously, IMHO I would not consider the draft of a bluewater boat to be either a make or break criteria for buying it.

I have noticed that here in the Caribbean there are a lot more hurricane holes available for shallow draft vessels. Expect that is the case in other parts of the world also.

[KJB]

Originally Posted by Eleebana

If safety and stability are the concern, then there is more to consider than simply draft as has been said before. You could have two identical boats, one with lead ballast and one with the same amount (in weight) of cast iron ballast and because the lead is denser the weight is concentrated lower, thus giving more stability.

The other thing I considered when choosing my current boat (in build) was how much all the stuff I take would effect stability. E.g. In a 42' boat I have 1100 litres water tankage (no watermaker). If it was a lightweight production boat, you'd be trying to get that all in under the saloon seats which are probably above the waterline level and thus adversely effecting stability. I have been able to have that tankage built in below the water line into the structural floors and I'm hoping full tanks increases the stiffness of the boat.

My boat has been designed to be a long haul cruising boat and the assumption is that we all bring too much stuff and this will effect certain designs more than others.

Greg

Greg, I think we're taking too much stuff - things just always work that way (we used to own a motorbus). I've seen some steel boats and a couple glass ones that provided tankage in the keel and throughout the hull - sounds like you have a well-thought out ship. Thanks.

[KJB]

[QUOTE=estarzinger;655848]the answer to that is pretty clear - the deeper boat will be faster, because (1) it can be lighter (less ballast) for the same righting moment, and (2) it will have less leeway going upwind.

Great answer! Short and precise - perfect. Thanks.

[KJB]

Quote: My reccommendation is that a 40' or so boat with 5'-7.5' of draft is pretty reasonable.

Quote: My feeling is that the moderate draft I mentioned above is a good compromise between upwind performance and general anchoring friendliness.

Thanks again Adelie. I'm beginning to like the idea of the moderate draft you defined so well. Understanding all things are a compromise - sounds like the best of both worlds.

Thanks for coming on board and for your extensive replies, it's what I was looking for.

[KJB]

Originally Posted by gbanker

4' of draft seems to work fine for our catamaran.

Seriously, IMHO I would not consider the draft of a bluewater boat to be either a make or break criteria for buying it.

I have noticed that here in the Caribbean there are a lot more hurricane holes available for shallow draft vessels. Expect that is the case in other parts of the world also.

Thanks. Enjoy the run!

[Mark Johnson]

Unless you plan to spend all of your time at sea, SHALLOW DRAFT IS EVERYTHING! IMO. I'm talking about 3' to 4'... It opens up so many really nice protected anchorages that the deep draft guys can't go. It is less of an issue in the Eastern Caribbean, (although I could often get closer to shore, upwind of the heard)... but for the US ICW, Gulf coast, Bahamas, Belize, Guatemala (up the Rio), Isla Mujeres, etc. you need shallow draft.

With the exception of "some" well built centerboard monohulls, the "well proportioned" multihulls are the only boats of this draft that can also be considered BLUE WATER. M.

[aquarian]

Originally Posted by atoll

having sailed once around the world on a 5" draft boat then another on and a half circumnavigations on my present yacht with 11'6" draft i would really reccomend a yacht with a shallow draft,ideally beachable.

this has nothing to do with the sea worthyness of the vessel, more the practical aspects of modern cruising,95% of the time is spent on anchor,all popular anchorages are full these days, a shallow draft vessel will allow you to go lots of places others can not,do you want to be part ot the 2% or part of the 98% cant go there?

I am with atoll on this one. My new blue water baby is an Albin Vega for exactly these reasons (3.8 foot draft) combined with proven ability, reputaion, and compact size. I don't want a huge boat because I sail solo almost always. Smaller is more corky, but much more manageable.

[aquarian]

Originally Posted by Adelie

In a completely rational world a shoal draft boat would be less likely to run aground. This is not that world. Charlie Wing in "the Liveaboard Report" indicates that there was an inverse relationship between draft and the number of times a boat had been aground. My sense is that in mild or settled conditions when consequences wouldn't be as severe skippers of shoal draft boats got a little complacent about water depth either sailing or anchoring. My sense is that in heavy winds or in areas where the bottom is rockier rationality takes firmer hold and the shoal draft boat is less likely to run aground. My conclusions extrapolated from what Wing wrote.

I can vouch for your assumption that we shoal draft sailors get slack. If the worst thing to happen is waiting out the tide, why stress it. I am guilty of knowingly going in too shallow.

[Bash]

Originally Posted by KJB

Example: Boat A and B are the same model, but boat A has a draft that is longer than boat B. Do both handle the open ocean equally well? I have come across this in my searches.

Any ideas?

The boat with the deeper draft will perform better to weather because it will sail flatter. Not only can it carry more sail, but it will need less rudder to correct for weather helm. This not only makes the boat faster, but also helps it point higher. An added benefit is that a boat with deep draft will make less leeway than a shoal-draft boat.

I have a buddy who owns a shoal-draft Catalina Morgan 44. When he takes the helm on my boat, he constantly sails around ten degrees too low because that's all the better his boat can do. When I finally convince him to harden up, he's amazed at how close to the wind you can get with a deep fin. We go through this every time he gets on my boat.

Some cruisers will tell you that they don't ever go to weather and/or they don't care how fast their boat sails. All they care about, I am told, is that their boat has good manners in a seaway and can stand up to a blow. Others, like myself, insist that a boat not only minds its manners but that it performs well across a variety of conditions. We are probably less likely to motorsail when harbor hopping simply because we don't have to resort to such tactics to make the next anchorage before nightfall.

You are welcome to join either group, and will find that we readily drink each other's cocktails once safely at anchor. When the shoal-drafters tend to drink more heavily than the deep-keelers, everyone seems to understand why.

[psneeld]

Funny.....again all the running to references and technical jargon.

No matter how a boat is designed...once sold...skippers cange the stability specs by boat alts and loading. What's the stability curves say about bicycles lashed to the lifelines? Who REALLY recalculates prior to getting underway?

Free surface effect is way more important than "static" stability info. if you don't have secured batteries or the straps holding your tanks in place have finally reached their service life...all the lead in the keel may mean nothing. Also...how much water have you shipped during that big storm that you should have missed anyway?


More US commercial fishing boats have flipped due to changes after initial construction than probably any other reason...coupled with getting underway with known leaks (free surface) and failing pumps...geeez...and people wonder why commercial fishing is so dangerous?

By a decent boat with a known reputation for bluewater passages and rig her right..pay attention to details and be careful of overloading.

Buy a boat with a draft that suits you needs...the wide spectrum is out there..and be a good skipper.

A good skipper can take a bathtub across an ocean, a good boat can save a bad skippers butt time after time...but a bad skipper? Nothing is safe from that.

[DoubleWhisky]

Hello
Before Bob Perry will explain all the things in few simple phrases (I must admit I really do admire his ability to do so), the loads of knowledge are to be find at the following forum:
STABILITY OF BOAT

[KJB]

A good deal of knowledgeable advice and sound opinions. This thread has done what I hoped it would, which is help define my perimeters in this area.

Good Deal!

Hopefully this will help some others as well who may have been wondering about this specific area.

Good luck all and thanks.