30' plywood sharpie

I like it. It brings to mind a remora.

 

Hmm yes, I think Remora's are designed for minimum drag on their host...



Cheers
Angel

 

Thanks for the catch Angel, yes, it was supposed to say "without" and is now fixed.

Bulbs don't lower drag, they raise it. Unless you can gain significant depth, so the weight of the bulb can dramatically affect the stability curve, they aren't worth installing, particularly on a shoal fin. The best thing you could do to a fin like that on the 40' NIS, is employ a "Skeel" effects lower edge or even simplier just a small end plate, say an 1" or so off the lower edge of the fin. Think of this as a aluminum plate, just a tad bigger then the bottom of the fin, of course attached to the bottom of it. It'll help with pressure bleed off and make the fin act like it's deeper.

Leeboards really are effective, but they clutter up the sides of a boat terribly. Twin center/daggerboards can be hidden in furniture in a 40' design, but frankly are a bit of a contrivance, unless looking for the last ounce of ability from the design in a shoal format.

 

Hello Ray,
many things have been said by PAR and Angelique and they are correct, I just want directly explain what my thoughts are for this design.


All the effort:
No big deal, designing boats is my wintertime leisure activity (hobby). Until now is not planned that the my design will be built as a "real boat" as I have other preferences for sailing boats, much more racier. I'am just fascinated by sharpies. Anyway, building a sharpie don't need special building methods, its all standart plywood and epoxy.


Model:
Yes, you are right, my model is 1/10th scale. For us "Metrics" its the logical choice, because we are thinking 1/10ths, sail areas shrink a 1/100th and volume/wheight a 1/1000th. Very easy to calculate, just take gr. for kg.

I have no problems with the wheight of the boat and the rc components. My "crew" wheighs around 220 scale-kg's, just as in real live I don't expect to have 1:1 sailing results like in a tank test, just want to see it sail and gain a few hints for design-spiral no. 5. Modelmaking is good to feel proportions and to check your design work if you can build what you have drawn.

Design:
In design my boat seems to look like the NIS Sharpies, but it isnt.

Compared to the NIS26 my design is much lighter ((2500kg vs 1600kg incl. trailer) and much cheaper to build. My bill of materials calls for 31 sheets of ply (roughly estimated), while the NIS 26 wants to have 63. (according to the NIS website, I dont know where they hide all that plywood.) NIS will become even more expensive, as carbon fibre masts will be standart on those boats in a few years. My shorter wooden mainmast (and the cheap OK Dinghy rig as a mizzen) is working together with a spuaretop mainsail (mimicry gaff) and should be a lot cheaper and nearly as effective.

The minimum depth with that short keel will be just under 2'. I'am experienced in flat water sailing (I sailed Jollenkreuzer for a long time) and in real live 1'10'' is just a small drawback against 10''. You can't beach your boat for long as the small waves and the sand will ruin your bottom, so you have to anchor in deeper water for the night anyway. You can not sail a centerboarder with the board all up, because you need the leeway prevention of at least a part of the centerboard. Kneedeep or ankledeep water, there is no big difference, you can walk ashore.

The advantages are massive: The boat can be much lighter due to the leverarm of the deeper keel. I'dont know how much ballast a NIS 26 needs, but I will have just 350 to 400 kg to have calculated positive stability for 120° without all the tricks (waterthight masts and reserve volume of the raised deck cabin). In the moment it is not decided what kind of board is housed in the keel, but the centerboard case will reach in no way more than 8'' into the cabin. Comfortable seating even for tall guys. (Look at the people on the website sitting in the NIS boats).

So thats it for today, see you soon, Michel

 

Seems you know what is needed for the planned conditions and use so your ideas should work for you. One problem with scaling in 1/10ths is that volume scales by the cube, thus Weston Farmer's long-used scale of 3/4" = 1' or one-sixteenth scale. This was for flotational use in appraising proposed designs, as it was very easy to scale up to actual.
Radio control use is an entirely different thing and quarter scale would work well for this little boat.
Sometimes I get to make cool models for other people and from my years at ILM doing ship models for pirate movies, one-quarter scale is best for believable effects that don't look like models, and one-sixth works if you push your techniques. This is because you can't make water drops smaller.
If I left the tank structure in the foreground off of this pic how many would think it a real brig, just coming to anchor with her sails aback in a hazardous situation?

 

220g for RC gear sound a little light. My 3-channel set ended up at 630g + frame, transmission mechanics and all.
___________________________

One often overlooked point to consider :
PAINT
-areas to be painted scale only M^2, and thickness (=weight) of painting is unlikely to be 10 times less; 3, may be 4 times, but not 10.
So in a small model weight of paint became quite a part of equation. One my 0.75m model hull, nearly DOUBLED her weight when painted .
Same is true for almost everything not left bare.

 

I would be fooled, for a long time.
In movie one can search for suspiciously static people, in photo there is no such obvious clue...

 

Yes, my point exactly

Been through it all before at

http://www.boatdesign.net/forums/boat-design/scale-model-power-calcs-26955.html

Also, how do you get a boat the same size as a NIS being so much lighter ?
have you had an engineer do the calcs ?

But since its all a 'fun exercise', its all moot anyway. I am in my 5th year getting a similar boat designed, certificed, and ready to build, so I have a little idea of what is involved.

 

Ok, see the picture below. The sailing winch is missing, because i just bought it and it's on the postaltrip now. But it will weigh in at 55gr. Did I forgot something? I don't know because this is my first rc experience.

I don't try to scale down everything up to the paint. The hull is covered with epoxy now and will get just on layer of transparent spray paint. If the Model is at 1,35kg ready to sail I will be satisfied, because this is the designed displacement. And I'am optimistic, at the current stage the hull weighs 364gr. Add 350gr ballast and 220gr for the rc, I have more than 400gr left for deck, rc fastening and rig.

I'am not building a exact tank test model, I just want to see the boat sail and want to know if i could build it ... and if my lines are harmonic.

Grreetings from the North Sea Coast, Michel

 

Dear Ray,

No, I did the calcs by myself. But if the real boat will ever be built, a pro-designer will check the plan, thats for sure. I'am not that stupid.

I can just guess why my design is so light in comparison to the NIS 26, because I have not designed my boat with the specification of the NIS 26 beside me, I followed my own way of thinking "sharpie".

One reason why my design is so much lighter might be the amount of ballast. Perhaps somebody here on the forum knows how much ballast a NIS 26 carries and whats her bare weight and displacement.

Next is the trailer. I estimated 250kg for it, don't know how much for the NIS Trailer.

Lower freebord and beam and just sitting headroom save some m² of surface for sure. My interior is designed around double longitudual backbones, these are also the bunkfaces (bunkrisers? sorry, dont know the correct word in english). This is pure raceboat structure on low tech level and save a lot of kg's. Most of the interiorparts built in will have structural importance and if not, they are made from 1/4'' or even thinner ply. I have no bookshelfs, backrests and equally expendable fairings you can see on the interior fotos at the NIS website.

As stated before I expect to need 31 sheets of of ply and even if you allow 5 sheets more because i have overseen some parts or calculated wrong, the NIS 26 calls for nearly the double amount of ply. All that plywood has to go somewhere in the boat. I would guess it goes into structure and accomodation seperatly and not as one part for both.

"Every part that is not built into the boat, has not to be built, does not weigh anything and costs nothing" Dick Newick (free re-translated)

My calclations are realistic, my old Waarschip quartertoner was quite similar in length, beam, scantlings and interior, weighted around 1100kg ready to sail and had 550kg of lead.

Grreetings from the North Sea Coast, Michel

 

Hé Lucky...

Looks like you forgot the attachment :idea:

Cheers,
Angel

 

Here's an ad on the NIS forum for a 26' that says... ‘‘Displacement 1800kg - Keel/Ballast Swing centre board with 550 kg internal ballast’’

Cheers,
Angel

 

fixed it!

 

People were put on model with digital effects.

 

Here's a few ideas of where the plywood in an NIS goes - how thick is your transom with a 40hp motor ? Have you allowed 4 sheets of 13 mm ply.

When you get around to insignificant detail like stability curves on a boat of that size, you will need around 500 kilos just like the NIS and the MacGregor 26 ( which is another 26ft sharpie) .

Your trailer will probably end up with a kerb weight of over 700 kilos, ( eg http://www.dunbier.com/index.php?option=com_virtuemart&Itemid=80 )

because of all the ballast - unless you go for water ballast.

Its a bit simplistic to gloat how much better and lighter your unengineered, non-professional design is when its all just a twinkle in your minds eye.