Can a ship tow a sail boat?

[oleman]

Almost all USN war ships ar equipped to tow other war vessels. Normally with a long towing lines (hauser) and at a few knots. Very slow process but all ships know the drill. Small boats around 35' could be towed from a boat boom or hoisted along side. Being found by a USN war ship is not a bad thing if a vessel is in trouble, they are very capable and never ignore a distress call. Even if your vessel is on the other side list they would still render aid.

[FlyingScot]

I don't claim to know all the particulars, but if I was out of fresh water, I would be gulping down a bottle or two as soon as offered.

[lord at sea]

The problem is not how it will tow, you secure the tow line to the base of the mast, the real problem is that once a vessel exceeds it's hull speed it can literally sail under.

[Lodesman]

Originally Posted by lord at sea

the real problem is that once a vessel exceeds it's hull speed it can literally sail under.

I'd love to see a video of this, or a scholarly article describing why this would happen.

[Auspicious]

Originally Posted by lord at sea

The problem is not how it will tow, you secure the tow line to the base of the mast, the real problem is that once a vessel exceeds it's hull speed it can literally sail under.

Originally Posted by Lodesman

I'd love to see a video of this, or a scholarly article describing why this would happen.

It depends, mostly on hull form. Depending on the shape, especially buttocks a hull can generate lift downward from water flow. That results in submarining. Lift also results in stern squatting. There are also dynamic effects. Too much pitch (remember: pitch, roll, yaw, heave, sway, surge) and the bow can bury in a wave and pitch pole. Then there are simple things like tow forces ripping the boat apart.



I think the text you're looking for is SNAME's Ship Resistance and Propulsion.

[Lodesman]

Originally Posted by Auspicious

It depends, mostly on hull form. Depending on the shape, especially buttocks a hull can generate lift downward from water flow. That results in submarining. Lift also results in stern squatting. There are also dynamic effects. Too much pitch (remember: pitch, roll, yaw, heave, sway, surge) and the bow can bury in a wave and pitch pole. Then there are simple things like tow forces ripping the boat apart.



I think the text you're looking for is SNAME's Ship Resistance and Propulsion.

Squat happens in shallow water - not so much in deep water. The hull form creates a little "lift" as it were, but there has to be an enormous amount of lift to overcome the buoyancy. Please don't point to the library and say "you'll find the answer there" - can you provide an actual article (from the tome you suggested or elsewhere) that supports this claim that towing a sailboat above "hull speed" will cause it to submarine?

[Don C L]

Originally Posted by lord at sea

The problem is not how it will tow, you secure the tow line to the base of the mast, the real problem is that once a vessel exceeds it's hull speed it can literally sail under.

Welcome aboard lord at sea!
I am pretty sure the speed must be a good deal more than hull speed to start to threaten the boat. I've gone a good bit over my hull speed and though there was a lot of bow wave and liquid commotion the boat did not take on water. However there was enough commotion that I am inclined to believe reports of displacement hulls being pulled down low enough to take on water... but like Lodesman, I'd like to find that reference.

[Auspicious]

Originally Posted by Lodesman

Squat happens in shallow water - not so much in deep water. The hull form creates a little "lift" as it were, but there has to be an enormous amount of lift to overcome the buoyancy. Please don't point to the library and say "you'll find the answer there" - can you provide an actual article (from the tome you suggested or elsewhere) that supports this claim that towing a sailboat above "hull speed" will cause it to submarine?

Squat happens anywhere. I think what you are referring to is the pressure reduction in very shallow water that causes ships and barges to be sucked down and bang on the bottom. That is far different from hydrodynamic lift that causes stern squat and generally isn't seen in sail boats.



Buy the tome and read padawan.

[Corvidae]

Apply enough force, and any boat will plane. Throw a basketball or a rock hard enough and they will plane.

It's all a question of applying enough force, without destroying the boat. That boat probably takes around 50hp to reach hull speed, and around 180 or so to start planing. The hull could handle the speed through the water, but attaching a tow rope is going to be a problem when it's going to have to handle short loads in the range of 33,000 to 100,000+ foot pounds. Every cleat on the boat in a balanced net of lines attached to a strong enough cable might be able to survive it, but there's going to be some damage.

[a64pilot]

No, not every hull shape will plane.
You can put a 300 HP outboard on a non planing pontoon boat and it won’t plane, but it will roll a tremendous wave.
I know your saying, well maybe it takes 1000 HP then, but I don’t think so.

I’m trying to tow a sailboat like this one at 14 kts, I believe drag would just go so high that nothing on the boat could withstand the strain, tie to the mast you’ll just pull the mast down as it breaks in half etc.
But that’s my opinion.

[StuM]

Originally Posted by Corvidae

Apply enough force, and any boat will plane. Throw a basketball or a rock hard enough and they will plane.

False analogy on several counts.
The basketball or rock are not starting at rest, semi-submerged.

Nor are they subject to a continuing vector force above their CoG and CoR while semi-submereged.

Nor do they "plane", they "skip".

[Lodesman]

Originally Posted by Auspicious

Squat happens anywhere. I think what you are referring to is the pressure reduction in very shallow water that causes ships and barges to be sucked down and bang on the bottom. That is far different from hydrodynamic lift that causes stern squat and generally isn't seen in sail boats.



Buy the tome and read padawan.

If you want to call it pressure reduction in very shallow water, then go ahead - most mariners call it "squat". What you refer to as 'stern squat' has little to do with Bernoulli-effect downward "lift", but is rather a result of the vessel building a large bow wave and pitching up on that - if you say that is hydrodynamic lift, then I defer to your expertise. Squat, as mariners know it, certainly does not happen to an appreciable amount in deep water. If you have the book, then please direct us to the section that supports this assertion that a sailboat exceeding hull speed will "lift" itself underwater. IME, a displacement hull above hull speed (I know you do not like this term, but it has its purpose) makes a massive wake, and is noticeably trimmed by the stern, but does not 'submarine'.

[lord at sea]

what gives you the impression that the mast would break, considering the amount of pressure that it has to endure while under a full press of canvas?
as to sailing under, there are several factors that come into play, first the seas are heavy or agitated, there is the molecular cycle of the wave moving upwards on one side and downward on the opposite, and a vessel moving in a fluid tends to create positive and negative pressures depending on hull shape and length, most of the bouncy being near the middle and less at both ends, so but loss of buoyancy and the tipping motion of the vessel, plus the wave molecular motion downward, and the excavation of the water and air in an agitated motion that reduces the buoyancy, makes for the vessel sail under .

[lord at sea]

given what you think , How would you be able to use an anchor for mooring or a sea anchor in a storm, if they were no able to withstand enormous pressure.

[Lepke]

Ships don't tow sailboats because they'd have to reduce speed to avoid damage to the tow. Moving a ship thru the ocean costs many thousands a day. If ship's ocean crossing costs several days extra running because of towing your sailboat, who pays for it? The insurance won't. And if they called a tug, that would be several hundred a day. And a tug gets paid for the trip out, too. So it's cheaper for the insurance to have the boat sink and buy you another one.
When I was in the navy and we rescued some idiot, we got to sink the sailboat with gunfire. (hazard to navigation) Lotta fun!