stability with speed

You may be right. I know it doesn't take a lot to stiffen up a canoe or kayak considerably. When I take a rest from paddling during a long (for me) trip my usual way is to stick the paddle across the gunnels and hook a leg on top. Then I can relax or even sleep, the boat feels rock solid even though the buoyancy of the blade is only a pound or so. Of course I can sleep anywhere in almost any position, genes from a naval family I suppose.

 

It is pure dynamic stability. At anchor I almost fall overboard walking from side to side in a 19 foot V bottom. At speed it is rock solid. I noticed years ago when I was in a flat stern round bottom canoe with a 9.9 outboard (fun). At rest it will tip over if you stand up wrong. Opened up you can't make it tip over.

 

The reduction of yaw with increasing speed is a design factor. It is not difficult to design a boat that trips over itself as speed increases. It has to do with how the center of resistance is affected by speed and yaw angle as well as the magnitude of the damping force and paddle cadence. The latter two generally do help reduce yaw excursions; but I believe it is primarily a design feature.

 

I believe that the design is of no consequence so long as it is symetric. I think that this subject is more related to fluid dynamics that hydro dynamics and I have no background in fluid dynamics.

 

I have no idea what design factor Phil is referring to, but my canoe which I designed and built shows very similar behavior in this regard to some of my other boats, although they are quite different in other respects.

The canoe has a skeg and it takes a lot of work to turn at any speed, or even at rest. It hardens up further under way.

My recently completed sailboat can also be rowed, and that also stiffens noticeably under way. It is the opposite of the canoe, short and fat, no skeg, and at rest it can literally be spun end to end with 2 pulls on an oar. When starting I have to be careful to pull evenly to keep her straight. However, once under way holding a straight course becomes much easier, and it needs several pulls on one oar, at least a half-dozen, to execute a full turn around.

The only thing I can think of which makes any sense at all is that the blade's force on the water decreases at speed, but I don't believe that is the whole story. Petros' vortex theory is the most likely explanation I have heard. The rowable sailboat has a single 72 deg chine and demonstrates the effect most strongly, the shortest of the kayaks has a rounded bilge but it has 2 sharp-cornered grooves along the bottom and it also shows the effect clearly. The canoe has 2 chines at 25 and 46 deg and shows the effect somewhat less.

My longest boat is another kayak which also has a rounded bilge but a flat bottom and I don't recall really noticing the effect on that boat, however in the interest of full disclosure I don't have a lot of time in that boat as the homebuilt canoe is a much nicer boat.

 

what is the best boat for stability and speed?

Great forum, need some help. Looking to buy a sailboat capable of world wide sailing with solid stability and good speed. I sailed plenty of friend's boats and rentals, but not sure what to buy. Is Beneteau good enough or I have to buy Swan not to sink in the middle of Pacific? Is 36 footer good enough or I need a 65 footer? Please let me know if you are an experienced sailor.

 

A mass production boat will not satisfy your needs, and a 36 foot is too small to make a sufficient liveaboard. Something in the 48´ ballpark comes closer.
And I would look for a metal boat, not plastic!

There is a saying on the barefoot routes: 50% of the circumnavigating yachts are metal, the others are US American!

Not all these silly comments are as stupid as it might seem.

Regards
Richard

 

off shore sailboat with good stability and speed

Thanks, Richard. That's a good start. But Titanic was metal, right? Isn't fiberglass a stronger material in case of collision? Metal rusts in salt water, doesn't it? Maybe someone can tell me why fiberglass is so bad, although the companies say fiberglass is good enough for blue water sailing. Would any metal boat do or I need top manufacturer? I know boats that sail into icy waters are usually metal. Any suggestions for metal sailboat company? Thanks in advance.

 

Titanic was metal right. But was a complete fault in every design aspect!

Fibreglass is the weakest of all common boatbuilding materials! It has advantages for the builders only, not for the customers. (I build in wood epoxy and Fibreglass too, so I know what I´m talking)

My own passagemaker could be easily built in my preferred material and method in wood epoxy, and it could be done in house!
But I prefer a steel built boat done by others! Being the 7th newbuild for my personal use, I claim to know what I am doing.
A metal boat is just the better choice when hitting a container or hammering on a reef for half a day. And that happens, no doubt!
Metal corrodes, thats right. Aluminium though builts up a thin layer of a corrosive which protects the metal from corroding further. In theory a Al boat will never corrode away. Just leave it unpainted and it protects itself.
Todays steel boats are coated with epoxy primers and epoxy paints to prevent from corrosion. When done correct, a steel boat is as maintenance free as a GRP one! WHEN DONE CORRECT !!!
A perfectly executed wood epoxy boat is a prime choice too, but I have higher latitudes in mind and need a icegoing boat, there Wood Ep is´nt the choice (as GRP definetively is´nt).
Well good enough to cross the oceans, GRP maybe, some have done it and survived. But from a technical point of view GRP is the worst material, period.

No, not any metal boat will do! Not any yard either!

Like in all other materials the building quality varies far too wide, to allow such a statement.

Recommendations are a bit a dangerous thing you know?
What is the length we are talking now?

Regards
Richard

 

good passagemaker with stability and speed

Thank you Richard, everything you say is confirmed by my research to be correct, and you sound like a great experienced sailor. I wanted something not longer than 85 foot schooner type, and not smaller than 42cc type sloop. My prime concern is safety as my family may be traveling with me. I heard steel rusts from inside, aluminum is good. Let me run this by you. Can a frame be made out of wood, with aluminum on outside of hull, and the whole thing fiberglassed inside and out? My thinking is strenth of wood and aluminum with low maintenance of fiberglass. I can be wrong, just an idea. Either way, I will be making a custom boat, not buying production fiberglass. Appreciate any insight.

 

nyalex - why do you want to glass a metal hull? what should that be good for?

and i do not think that it would be a good choice to mix wood with metal...
i know that metal is/was always used to stiffen a wood construction but you do not use wood do stiffen (frame) a metal construction... wood is not as strong as metal and therefore the weakest link...
no good option to me...

thats a good one...

for me aluminium is the choice... if it would not be that expensive....

 

Every material mix is a danger (except wood epoxy).

Aluminium and wood may be the worst possible combination! Al corrodes immediately away when it is in contact with "standing" water.
Glassing metal is just adding weight and trouble! But covering steel in epoxy is a proven (and worldwide accepted) way of making it rust resistant. A correct built steel boat does NOT corrode!
Of course a proper maintenance schedule is very important, but that is valid for EVERY material.
When you scratch a GRP hull you need to repair that immediately, or it gets you in problems. Same is valid for any other popular boatbuilding material.
The only maintenance free material is Titanium! That would be the best available material to build a boat. But it would cost more for the hull and deck alone than for a complete boat built of other materials.
Aluminium is NOT more expensive than steel, when the yard is very experienced, or better specialized in Al, and the design was made for Al exclusively!

You know between 42´and 85´is a difference of several million $$? And handling a 85´boat with family crew can be a task, even for the skilled boater. On top of that, you can reckon one person for each 20ft above some 60 or 65´ for permanent maintenance work, just to keep the boat in good condition! They are not part of the "sailing" crew, just in charge of service.
So, my advice would be, get familiar with a reasonable size of boat, say 65´as the absolute upper end. 50´the lower...(still a large boat)

Regards
Richard

 

stability and speed

Thanks a lot, guys, I appreciate your input. Seems like custom made aluminum about 65 feet is the way to go. Monohull? I sailed catamarans, but not in the oceans. They are fast, but are they stable and fit for world wide travel? Also, I heard that racing boats made out of fiberglass race in the oceans with success and even circumnavigate as well. Would such a racing boat be good, I don't know many racing boats, may be something like Beneteau First series. Are they better built than cruisers? I really love sailing, but no way I want to sink like some have in the past. Especially with family onboard.

 

The best racing vessel (no matter boat, plane or car) is the one that falls in pieces right at the chequered flag!
And the manufacturer you named is doing mass production for the charter market! You may find the answer yourself.
On multihulls I cannot comment in deep, I am biased against them. I would not take one when given for free.

Regards
Richard

 

That's true, although there's a lot to be said for a little over-building, just enough for the crew to get off ...