How to determine a 'heavy boat'

ChrisE said:
The easiest indicator is the cloud of flies over boat, the second is that unique smell below coming from years of leaking bilges, the third is the dark interiors that would look amiss in Stalag 17.
Click to expand...

:D:D:D:D

Whereas my plumb-stemmed, flat bottomed, stuck-on keel (if it hasn't fallen off) boat is so terribly twitchy that disaster nearly befell me when I forgot to set the autopilot when going below for a short break. Came back up to find her charging along nearly five degrees off the course that I had left her on. :eek:
 
michaelchapman said:
Supposing you have two boats with the same water line length, same beam and both with a similiar reasonable hull shape.

If one is 50% heavier than the other, does that mean it needs 50% more sail area to go at the same speed?
Click to expand...

Don't think it's linear. However, 50% heavier means 50% more volume below the water line which in turn means a sharp increase in drag which in turn means more power and more sail needed. And thats ignoring the effect of wave formation which also needs more power.
 
alan_d said:
An interesting and informative read.

However, "I wouldn’t want a boat whose beam exceeded three times its length" brought me up short. Were you thinking of something like three cats rafted up?
Click to expand...

Yes, I know, I really should get in there and fix that typo! One third is what I meant to say, not three times.
 
The biggest issue with working off published weights for yachts is that the weight figures are generally innaccurate (though not always). A weight needs to be established for the lightship condition, ie no extras, fuel, water, spares, stores, safety equipment, etc etc, then add these on, it is also difficult to establish whether sails, furlers etc have also been included in manufacturerers data. You will never get these answers directly so you have to adjust the figures yourself hence if you are only weekend cruising your boat will be quite different to the same boat well prepared for an ocean crossing.The smaller the boat the bigger the impact of all the food etc etc. Nigel Claders book does sum up boat differences very well even though its probably a little old fashioned now in its viewpoint. ' Boatowners practical and technical cruising manual
 
Talulah said:
Some thoughts but not directly related to length, beam displacement etc:

Slamming:
Slamming is exaggerated by designers pushing the waterline length further forward. Not for performance but to increase the accommodation up front. The consequence is a flatter hull. To avoid slamming look for bows that are angled back. A lot of modern boats have a vertical or almost vertical bow.

Maintain a steady heading:
For performance stick a big weight on the end of a very thin keel. All the weight is then as far as it can be for performance. However, the stick between the bulb and hull is now so thin it doesn't add any stability to the steerage and so the helm is constantly at work. A long keel with a bigger wetted area is more stable. Your Moody can easily be trimmed to require no input from the helmsman.

One thing I like about our boat is the encapsulated keel. Expensive to do for the manufacturer but great in terms of less worries about grounding. A number of modern boats will distort significantly if sitting on their own keel.
Keels that are bolted on after the boat is manufactured make boat manufacturing much cheaper. The hull is at walking height rather than everything having to be done from a gantry. However this keel makes for a slower boat.
Click to expand...

Just completed trip to Corfu from Marseille. Most down wimd legs completed in big seas and 25 to 35 knots of wind. The boat is a Westerly Oceanlord. One of the interesting things was that although she was easy to manage even if over canvassed, if we were logging 8.5 knots regularly (average) then the GPS only showed distance travelled of 7. Analysis of the GPS track showed constant S bends. We were steering as accurately as possible.

Now compare this to my last boat - a Victory 40. on several occasions we logged an average of 9 knots on the log and on distance travelled (long enough for tide to cancel out) The explanation is she went straight as a die - we never steered her as she did better.

So Moody Nick - add this to you list..... In a way she was a better boat thn the Oceanlord - but both were built like brick ****houses.
 
Bosun Higgs said:
Don't think it's linear. However, 50% heavier means 50% more volume below the water line which in turn means a sharp increase in drag which in turn means more power and more sail needed. And thats ignoring the effect of wave formation which also needs more power.
Click to expand...


I know its more - however given the same length and a decent shape in both cases (then the wave formation is not an issue), my intuition says that it is less than 50% more power is required. But logic says it should be 50% more.

I can't help feeling I am missing something - why should it be anything other than linear?
 
michaelchapman said:
..... I can't help feeling I am missing something - why should it be anything other than linear?
Click to expand...

Just a thought; the drag formula corresponds to a power law. If there is another power law for lift generated on a sail then the difference between drag and lift indices may be where the non linear relationship exists. Anyway, I have no idea, just a thought.
 
Chris_Robb said:
Just completed trip to Corfu from Marseille. Most down wimd legs completed in big seas and 25 to 35 knots of wind. The boat is a Westerly Oceanlord. One of the interesting things was that although she was easy to manage even if over canvassed, if we were logging 8.5 knots regularly (average) then the GPS only showed distance travelled of 7. Analysis of the GPS track showed constant S bends. We were steering as accurately as possible.

Now compare this to my last boat - a Victory 40. on several occasions we logged an average of 9 knots on the log and on distance travelled (long enough for tide to cancel out) The explanation is she went straight as a die - we never steered her as she did better.

So Moody Nick - add this to you list..... In a way she was a better boat thn the Oceanlord - but both were built like brick ****houses.
Click to expand...

Ok then this is my analogy.

I don't understand all this physics, maths and pontification. This is my equation to heavy boats.

I chose our boat because I liked it's lines, the build quality, the nut and bolts of her, the sea kindliness of her and the comforts that goes with it all this. Since we got the boat we've never felt unsafe even when caught in a f10.
We sail ours as a man and wife team with no probs till it comes to berthing and this can be tricky in certain weathers. The draw back with as with so many big keeled (ours is not a long keeler) is going astern, god bless bow thrushers.

We own a heavy 50ft S/Y, 24t including 8t of encaspulated keel. Light winds no chance. Over ten we're sailing, except when to windward which we struggle with on anything less than 40 degrees unless we have a good blow and we might just make over 30.
Beam reach 8/9kts in f 3/4's. Quickest we've ever done is 10.5 knots reefed well in a
f 7/8's blow.

If you like what you are looking at and not wanting to race or rush somewhere whenever you go out, what's the problem just follow your heart. You can always chat with other owners of the type you are fancying if you have doubts.

If you want a plastic fantastic, buy one, I've had'em but I like the heavies. At the end of the day it's a personal choice because no yacht ticks all the boxes it just needs to tick yours.

I nearly bought a Oceanlord before this one turned up. The wife calls it fate......!

_____________________________________________________________________________
 
You must log in or register to reply here.

Share this page

Top