Aluminum "Shoal Sailer"

this is a star 22 aluminium sailboat. I don't know where you read small boats should not be aluminum. That's ridiculous.

 

As per flat vertical sides and lifting board: Bolger wrote that his designs of that configuration sailed at about 10-15% degree heel therefore, boat would sail better if boards at each side built slightly inward to be vertical when sailing at average heel.

Re: dead flat middle third lengthwise.
When you move from vertical sides to a dory proportion of about 55% bottom width of BOA at mid section and also keep highly flared ends, lengthwise you can remain deadflat entire length (eliminate rocker) and still tack decently. Chinerunners can be wide as well.
Either way if designing a boat this way, my preference would be for pointy ends (reason being - easy to balance) and follow the well known fact that a good sharpie has L-B ratio of a minimum 4-1 and same if going the dory route

Dory type hull will be almost twice the draft w same displacement

 

Wow, didn’t expect so much interest, great!

thank you for the suggestions. I like the idea for chine rudders, and am thinking snout using chine ribs for protecting the hull and adding some lateral (if not also rearward) resistance.

In terms of using someone else’s plans, no way. I’d rather fail in disgrace than follow a beaten path. I appreciate that the smartest thing to do might be to buy a boat right now and go sailing in it tomorrow, next might be follow a proven design and get someone more qualified to build it... nope, conscious decision is to pursue the unknown, learn, and be satisfied with mediocre results that are the direct result of my effort and imagination.

I can’t comment on the merits of the other design suggestions now because I don’t know enough about them and also may misinterpret them.. I spend enough time on skype to be wary of even the most eloquent descriptions... they can still mean something else to each interpreter. pictures are good though!

Regarding the last post of line about stability simulation - I forgot to point out that approximating the hull with points was only a stop gap effort to try to achieve real-time calculation. It was not sufficient. That means that going forward it will be just as well to utilize the full accuracy of the manifold brep(s) below the waterline. The step amounts for each parameter can also be decreased once narrowing in on a final design. I’m looking forward to getting into the hull design tools, we can try some of the suggestions and see effects on stability at least. I appreciate that CFD simulation takes experience and discretion. This static stability stuff on the other hand is too simple to screw up too badly (free surface effects not included).

Thank you again all for interest and input, cheers!

 

If you rather fail in disgrace than follow common sense, then go for it. Please post videos of the boat sailing. Good luck.

 

Th

Thank you!

 

I had to smile at the "beaten path" part. You do understand that the SOR guides your choices and the resulting boat will look more or less like any other with a similar SOR.
Just to give you some examples: the weight-draft limitations will push you to a flat, wide underbody with plenty of form stability. Your choice of lateral plane is centerboard (single or double) or leeboards. Your rudder will be either pivoting or barn door, but always transom hung. My advice is to loose the attitude and look at designs with similar SORs. See what has been done and what is usefull for your situation and what you can live with esthetically.
To give you some inspiration take a look at the work of Lucas. For example his Mini CP Mini CP http://www.fr-lucas.com/mini-cp-1591 or the Birvidic 700 Birvidic 700 http://www.fr-lucas.com/birvidic-700-1625

 

I call it the "hexagonal wheel syndrome". It states that it is better than the round ones because it is novel and original.

 

Rhino has the Hydrostatics command which provides direct calculation from a NURBS surface hull model of quantaties needed for hydrostatic analysis. Rhino also has command for directly calculating areas, volumes, centroids, moments, etc from NURBS surface models.

 

"I did it my way" worked for Frank Sinatra, but probably less so when dealing with the laws of physics.

 

(not sure if the links here will all work correct, so best navigate the site yourself, which method also shows much more of Dick Zaal's work)

See for alu shallow draft ± 10 m (33') LOD eg. Dick Zaal Yacht Design → Designs → Aluminium → Center Board

Dick Zaal Zeevink Multi Chine design № 55 b ↓ check there the links - 'specs' - 'images'-





Dick Zaal Zeevink design № 56 ↓ check there the links - 'specs' - 'images (exterior)' - 'drawings' - 'pictures (interior)' -











Dick Zaal Swift design № 57 ↓ check there the links - 'specs' - 'images' -

 

Yes, Rhino is awesome. The latter functions are also available in the scripting components and I'll definitely use them instead of the ghetto point counting method!

 

Those look nice, thank you. The forward canted rudder is interesting.. I was wondering about how they might work with the pivot vertical or otherwise aligned with the centroid/COE.. to get the balance without a forward notch or spade style connection.. I'm sure it's been done.

For lake sailing, I am unsure about the desirability of the canoe stern. No doubt they are beautiful and seaworthy. The reasoning is that when you are in a position where the boat is really dragged in over shallows/reeds, it can be handy to be able to push it out from the rear and hop on.. as to whether this is permittable in seamanship or not, we'll leave it to the peanut gallery to comment, simply it is a consideration for me.

I appreciate the links and am checking all of them, thank you!

 

Part IV - Hull Design Tool

Here's about as far as I've gotten now.. making a parametric hull model.

This uses Grasshopper with python scripting to generate the main panels of the hull, at this time the transom has not been included yet.


The numbers floating around are just the bounding box vertices, to make it easier to reference them.

The panels are made bow to stern, top to bottom. More specifically, the topmost panel is defined by a spline defining the top perimeter, and then a developable loft is made between lines normal to that spline at the bow and stern. The panels shown above look like this when flattened:


So the basics are there for laying out the panels for cutting someday.. they will need to be cut down more to fit real sheet sizes.

Right now the hull model has three panels per side, and based on the suggestions to try a two panel approach, I'll make a version to handle that too.

One thing in the picture of the "Ovni 395 sitting happily on the sand" sent by bajansailor which I really like is the flat bottom panel.. and playing with the hull model I think I see why it may be a good idea (besides the benefit of allowing the hull to sit flat which is great)...
As the entry angle of the lowest panel is decreased it bulges downwards like crazy, so cutting and capping that off with a flat panel makes sense for controlling the draft while sharpening the bow.


Overall, yes, I suspect my boat will end up looking a lot like that Ovni 395, (looks almost octagonal too no ? thank you again for sending that information bajansailor!

Anyways, pretty busy this week so might not be able to update, but the plan is to make a two panel version of the hull design tool, as well as an option to include a flat bottom panel like the Ovni has. Then will be on to playing with the hull design and trying to consider the forms it might take.

I am planning to design considering a normal ideal heel of 15 deg upwind.

One thing which I would appreciate input on is what yaw angles should be sought/expected while beating.. I understand that about 3 deg of lee rudder, resisting weather helm, is a good trim (I think I read that in 'Sail Like a Champion'). Does this mean that there is 3 deg or less of yaw ? more ? I have no idea.

I want to position the hull at 'X' heel and 'Y' yaw, 'Z' pitch, and consider the motion/hull geometry moving through the water at that orientation.

Also need to consider underwater appendages.

Thank you again for interest and constructive suggestions/information! Take care!

 

This explains the 6 axis movement of a boat. Yaw, depending on conditions can be a lot more than that. Even on a strong breeze with 6 to 8 foot waves, a boat that size would yaw more than 10 degrees going upwind.
Term https://www.wartsila.com/encyclopedia/term/ship-motions

 

How do you plan to obtain developable surfaces? Remember all developable surfaces are ruled surfaces BUT not all ruled surfaces are developable surfaces.