My boat any comments?

what of I put fin in front of the keel, maybe it would make stearing easyer? What do you think about it?

 

I think you should model it closely to known performers within the envelope you would like the boat to be. This keeps you off the design limb, so to speak. Playing with multiple appendages, hull shapes, sail plans and other major elements of the design requires much experience to do reasonably well.

Basically you have a big planning dinghy and should stick to that concept, save the forward appendage for another design. Personally I still don't know enough about the design, but general observations of the two drawings.

If you want a fun to sail (double digit speeds) easy to build boat, try a sharpie, built to traditional proportions. They go like sin, are about as cheap as you can get and will embarrass all but the racers on the lake.

All boats painted black look cool, they need a gold cove stripe though.

 

Since when can you get boats in different colors??? I thought they were all white?

 

Just a note, black boats get very very hot in sunlight. This might be a consideration with plywood. Heat, glue and water... never a good mix. White on the other hand is much cooler. You might consider a natural wood finish, that can look really nice too. What if you put in a few chines, so there is about 10 degrees between them, rather than 70 degrees as you have at the moment.

The problem you face is that to keep it flat you either need rather fat crew sitting on the side (this may not be a problem, I don't know) or a canting keel. Canting keels are excuses for the boat to leak, and fat crews mean that the boat is inefficient single-handed. Considering that we were heeling around 25 degrees on every boat I sailed at Cowes Week (with several people on the rail) I'd still suggest you round off the bottom at least a little.

netjaws, you're comment about running the hull at a heel angle to give a perfect tri-angle may reduce wave drag, but since the boat will have a lee-way angle (which may be considerable) the amount of drag from separation over the sharp edge really isn't worth the hassle.

Tim B.

 

This morning I woke up and understood that my boat isn't as good as I thought then I was drawing it. It would never sail completly flat. I think I will add one more chine or do it like star class sailboat. What kind of heel angle should I look for? I am thinking about 10-15 degrees. Am i going in the right way?

 

One mmore pic of my older version of my boat (flat bottomed)

 

Take a look at Marc Lombard's Randonneur 550. It has a narrow flat bottom with two chines on each side:
http://www.boatplans-online.com/studyplans/R550_study.htm
http://perso.wanadoo.fr/marc.lombard/r550.htm (french)

You should calculate rightning moment for some angles of heel and compare with anticipated heeling moments for some wind speeds. Caluculate for light boat and with crew.

 

thank tou very much I got few Ideas from that website

 

MY friend, it a really really very good work!!!
You have plenty of talent!!!!
Keep on

 

I think I will redesign it..It would me much simplier to built it less then 8m long..I think it would be nice to bult it about 6 meters, basicly it would be a small dingulike keelboat with two sleeping bunks in front part of the boat, basic all the proportion would be the same, only outrigers willl be fitted alongside the cocpit. It would be daysailer with capabilytie of short weekend trips. 3 people, would be the best crew. Then the boat is built it could be fitted with genaker pole or something like that. I think about short keel, because it would be nice to go camping near trhe shore, and short long keel would make boat easyer to handle.

 

Don't give up on the flat bottom just yet! Whilst Tim B said the boat would sail flatter if you rounded off the chine, in fact the opposite is true. By rounding off the chine, you are removing volume (and wetted area, which is the plus point) from the point furthest from the centreline, which means you are losing form stability, the principal reason why sharpies have better initial stability than any rounded bottom hull of identical waterline beam. A deep bulb keel will take care of heeled and ultimate stability, although it moves the boat away from the sharpie trait of thin water sailability. Sailing the boat heeled by only a few degrees will present a V to the water, aleviating somewhat the pounding associated with the flat bottom. There is also a school of thought that says the immersed chine and flat topsides help reduce leeway - Phil Boger swears by this idea, and Matt Layden has built a few small sharpies without any centreboards which had shallow wooden rails running along the chine to act as 'fences' to the flow. I think simply rounding the chine a little would therefore be more effort than it was worth - you would lose some wetted area, but would also lose initial stability, and the resistance to leeway provided by the chine (which might let you reduce the size of the keel, resulting in the same wetted area reduction as if you had rounded the chine...!). A small radius will still mean that the forward bottom will pound, as most of it will still be flat. However, despite this part of the bottom not being particularly efficient in terms of dynamic lift, any flat bottom is better than any rounded or vee'd bottom for dynamic lift.

If you want a radius chine design, you need to go to a reasonable radius, which will allow a good reduction in wetted area. Look at Dudley Dix's designs, which incorporate a shallow v bottom below the radius.

I think your boat would do better as it is, unless you are willing to go for a large radius chine, or a properly curved bottom (like the Backman 18, which still manages the ply sides - it looks sweet ). Your boat is a different concept to most existing boats today, but then other than Ray Hunt with his 210 design (which is very quick and slippery), nobody has afaik Attempted to design and build a sharpie with a deep bulb keel. Without a comprehensive VPP analysis including the modelling of hitherto unmodelled features such as the potential wave reduction TimB noted and the leeway reduction I mentioned, there is no way to tell. Furthermore, sharpie hull forms are so removed from the Delft series that you would need to tank test a series of flat bottom hulls first to get VPP results you could believe. I think the boat would certainly be quicker than 'rounded' boats in some conditions, but it would also suffer a bit in others. In short, the performance profile would be completely different, and thus any optimisation of rig, foils etc would also go in different directions to that of more regular hull shapes.

I should point out that I don't have any bias for either type, although I think that there is so little research into keel ballasted sharpies that it is very difficult to draw any conclusions....if you go with the current design, it would be very interesting for the rest of us!!!

Andy

 

No I didn't say it would sail flatter, Andy. I said it would sail faster. My comment as to heel was that it would be nigh-impossible to keep a flat-bottomed boat of that size upright enough to make use of the flat bottom.

Downwind, I'm not arguing, a flat-bottomed yacht will almost always beat a "Normal" yacht. However, Upwind you'll find there's more wetted surface area and probably seperation over the sharp edge. Wave-making wil be reduced a little by the sharp corner.

tamkvaitis, I think this design has the potential to be a lovely cruiser/racer type. At 8m it is a good size, and gives enough performance without having to worry too much about building it out of exotic materials. 6m I think you would find is very much "between sizes" in that it isn't a dinghy, yet it's hard to fit all the stuff in for a cruiser (heads etc.). In terms of building it, anything over about 4m won't fit in a double garage (or not one with a bench in it) you might, perhaps squeeze 4.5m in if you're lucky, but you won't be able to get around it. Point being, 6m won't fit either, nor will 8m. Consequently you'll have to build some extension / workshop, so why not do it properly and make it house the 8m boat.

I really like the boat as it is at the moment, I'm just wondering if the effort saved in using a chine hull is going to impact more than you'd like on the performance. Of course, if you'd like to pay me some money and give me the hull geometry, I'm sure I could see my way to doing a few CFD runs. It would probably be more than you wanted to pay though.

Good Luck, and keep at it,

Tim B.

 

then i thought aboput this boat i looked at skiff's, then remembered a book witch i have red (voyaging on a small income) i liked the idea of a flat bottomed boat. I wanted to enter a bigest local regata, main courses are downwind, so the design concept fitted me perfectly. It is changing every week. I know that my boat don't loook like skiff at all, but this concept fits me. I like dudley dix'es concept of radius chine building, i have redesigned my boat (made a sketch), of a slightly wider boat with radius, it looks nice, but the building get complicated, I might loose downwind performance too.

 

Read "The Gougeon Brothers On Boat Construction" if you can get hold of it. It's a good book and pretty much tells you how to build any hull-shape.

Tim B.

 

Sorry Tim - I took your comment "Considering that we were heeling around 25 degrees on every boat I sailed at Cowes Week (with several people on the rail) I'd still suggest you round off the bottom at least a little" to mean windward sailing, and that rounding off the bottom might somehow help with stability...I cant imagine sailing consistently at 25 degrees heel unless it is to windward, as it's not an efficient angle of heel for downwind sailing (except in a couple of rare circumstances). I see now that you meant that the flat hull bottom wouldnt be providing much dynamic lift at this angle. I am sure you are right about the separation issue - thats part of why sharpie sailors have and are experimenting with bilge runners. I have read reports in Wooden Boat and on the web by owners of sharpies who state that they feel the leeward chine "dig in" as the boat heels, helping counteract leeway.

I think one of the important things in sharpie design is to aim for a smooth shift of the centre of buoyancy (within the constraints of a flat bottom) as the hull heels. Many people have commented on the behaviour of vertical sided sharpies in this respect - they let go suddenly and quickly unless backed up by sensible ballasting. Reuel Parker advocates flare in the sides of sharpies for this very reason, but too much flare may increase the flow across the chine Tim mentioned, amongst other things.

Tim is also right about the extra wetted surface, but then sharpies are designed around very different parameters to round bilge boats. They are typically lighter (being unballasted), and thus shallower, meaning that (as john Teale has noted) they need to be narrower to keep enough lateral hull area to prevent the performance from getting too 'skitty' on the surface of the water. These factors reduce wetted surface, and also meant that they were designed with low freeboards (to reduce windage and the centre of gravity) and moderate sail areas with low centres of effort. The shallower hull forms also had lower wave making resistance, meaning that the boats planed easily.

The interesting think about Tamkvaitis' boat is that I am guessing he is planning a ballast keel? This mitigates against some of the above, and certainly moves his ideas away from the sharpie rules Chapelle formulated.

A final note about flow separation: I noticed the last time I was on a Sigma 38 in a seaway sailing to windward that there was considerable flow separation across the centreline of the boat as we beat to windward, particularly as the boat was yawing a lot, so it exists on many round bottom (especially veed centreline) boats too.

I think this is still an interesting project - my gut feeling woulld be with Tim that the performance might not match hopes, and on this count I would perhaps go another way. But it would be easy and quick to build, and as i said before the parameters involved and the interaction of the elements are so different to current trends that you might be surprised - I'd have to say give it a go! Incidentally, have a read of Reuel Parkers "The Sharpie Book" if you are serious...the info is really about unballasted sharpies, but it would help with your perspective and there is some good building advice in there too.

Andy