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Old Mar 27, 2015, 02:18 AM
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Designing a 36 600 Class Yacht

I recently joined RCGroups and wanted to share my latest project.

I currently have a Northwind 36 build to the 36 600 class rule. It is a fast boat, especially to windward, but the hull form is somewhat old fashioned, and it could be quicker popping up onto a plane going downwind. I thought I would try to make a design that could outsail my current boat and still comply with the rule. After looking at the specific guidelines for the rule on the internet I began working.

I have based my hull shape off of Juan K's Volvo 70 Groupama, so it is radical, dishy, and very flat with a hard chine and lots of flare aft. Here, I have attached some preliminary renders of the hull and a CAD lines plan and basic sail plan.

The specs for the boat are:


LOA: 36"

Bmax: 9.732"

DWL: 33.708"

Displacement: 5.12 lbs

SA: 600 in2

SA/D: 22.44

Cp: 0.544

GMt: 0.493'

Wetted Surf Area: 1.43 ft2

LCB: -3.716% (16.764")

I plan to build her from epoxy and fiberglass (or possibly carbon fiber) matting and then race her against my current boat.

Things I want to avoid carrying over from the last boat are the blunt bow sections forward, the leaky servo compartment, and the low open cockpit that gets swamped when its windy.
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Old Mar 27, 2015, 08:31 AM
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Keep in mind, the VO70's (and similar) have a hull optimized for off-wind sailing. There is a lot of stern surface area designed for downwind "surfing", and unless you have strong winds, and a lot of off-wind legs, I think you may be disappointed. Simply look at the current ideas for some of the larger and most popular classes and you will see a hull shape that is fast - and most are really "Skinny" in width. IOM, Marblehead and RG65's all are following designs which have shown a good deal of speed over up wind as well as off-wind legs.

If you proceed, keep your build light weight and don't add too much weight, you may find your design faster than the "base" boat design, it will look pretty cool, and I am only pointing out the thoughts and ideas currently in fashion for a boat hull good on all points of sail.

Good luck with the design and build.
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Old Mar 27, 2015, 04:27 PM
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I am aware that most of the popular classes are heading towards narrow designs. I fully expect my current boat to out sail the new design upwind in light air. I usually sail off of a boat in an anchorage and more often than not I have ended up with too much wind rather than too little, hence the design for this boat. The extra righting moment provided by the hard chine and reserve buoyancy over the waterline due to the flare of the hull will make this boat more powered up and flatter in high winds in reaching and running conditions. Note also that when the boat heels, the shape of the hull is such that the waterline plane decreases in average width and the forward sections, due to the second hard bilge on this hull, become finer as the bow knuckle immerses. The waterline length matches the LOA for this boat upwind meaning that even for a 20% loss in upwind speed due to the wide transom, this boat should still maintain speeds of 1.85 knots upwind using the quick 1.34 hull speed rule. Even my current boat does not pass hull speed to windward, and at 100 percent of her hull speed (using 1.34 again), she is moving about 2.18 knots. I am aware that the 1.34 rule for hull speed is not as accurate as other methods such as Gerr's displacement speed formula, however I have not yet done calculations for both boats to figure maximum speeds.

I have been careful to monitor beam at the waterline and have looked at heeled waterline sections for this yacht. My Cp, which is a moderate 0.544 is intended to be suitable for a wide range of wind speeds. Prismatic coefficient, wetted surface, and sail area to displacement are the most important aspects of a yacht to consider in light air, while in heavy air, stability and sail carrying ability are more important.
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Old Mar 28, 2015, 02:57 AM
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impressed..........look forward to see more.

Very Much Interested To See....Hope You Share Your Progress. Kind Regards,Dean Derusha
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Old Mar 28, 2015, 03:08 AM
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Derusha: Will do! I am planning to purchase some balsa wood sheets in the near future. I have all the other supplies needed to make a plug.
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Old Mar 28, 2015, 12:32 PM
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Here's a modded 36/600 for sale:
http://www.rcgroups.com/forums/showt...8#post30636617
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Old Mar 28, 2015, 04:33 PM
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Quote:
Originally Posted by Scratchy101 View Post

This is the same class of yacht I have currently, although I don't have the modified bow. I made some changes like adding carbon main and job booms as well as carbon sails, new servos and a spectra headstay.
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Old Mar 28, 2015, 05:01 PM
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Not sure where you are located, but you should know that the 36/600 is basically a U.S. only class that is pretty much dead on a national basis. I believe the only area where these boats are regularly sailed is Arizona (but there might be a few other local activity pockets left).

In all events, the Northwind was never a competitive boat in the class and not a good reference for designing a boat. Also, none of the recent, racing 36/600s are built from mat, they are generally carbon or Kevlar cloth and some of the more sophisticated boats even used pre-preg.

The best advice I ever got was to find the local r/c sailing club, talk to them and sail/design what they are sailing. If your goal is to just to build something to satisfy yourself, please carry on, otherwise your efforts might be better in another direction.
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Old Mar 28, 2015, 05:09 PM
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I see your point, but since I live on a boat in New Zealand and am regularly moving around I have never come across any RC racing fleets. I am mostly aiming for a boat to satisfy myself and sail for fun. For the most part, I am only designing in accordance with the rule as a challenge. I am studying yacht design and want to see some of my work realized and at this point the small scale is more feasible than a real dinghy or some other craft.
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Old Mar 28, 2015, 05:52 PM
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There is very active r/c sailing in New Zealand. Take a look over at the IOM thread and you should find a number of clubs and builders/designers. There is also a NZ r/c yacht racing website. In fact, one of the best r/c boat designers and sailors Ian Vickers, is in Auckland Besides r/c boats Ian has been with a number of America's Cup campaigns....
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Old Mar 28, 2015, 09:04 PM
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I suppose there would be quite a few clubs here. Sailing is a very big sport in NZ
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Old Mar 28, 2015, 10:29 PM
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Does anybody have opinions on dual rudder systems? Do they work? I don't think I will go with one despite the fact that the end plate effect against the hull would be lost when heeling upwind with a single rudder because of the added complexity, but I still would like to know if its feasible.
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Old Mar 29, 2015, 10:41 AM
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May want to visit the web page for German company "Stockmaritime" - as they had done these including canting keel. Don't be shocked at prices !

http://www.stockmaritime.com/modellb...?modellbau/437

http://www.stockmaritime.com/modellb...?modellbau/436
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Old Mar 29, 2015, 04:08 PM
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Quote:
Originally Posted by Dick L. View Post
May want to visit the web page for German company "Stockmaritime" - as they had done these including canting keel. Don't be shocked at prices !

http://www.stockmaritime.com/modellb...?modellbau/437

http://www.stockmaritime.com/modellb...?modellbau/436

That's defiantly very cool. I am not planning to do a canting keel- the added expense and complexity are above what I want to spend. I am considering a dual rudder through for better steering efficiency.
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Old Mar 30, 2015, 10:12 AM
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One thing to be aware of, not a criticism of your plans: in R/C boats, especially those designed for informal sailing, hydrostatic hull balance (decoupling of roll and yaw) is a factor. This is because radio sailors often have to take their eyes off their boat to attend to things like not falling in the pond, and having your boat suddenly careen off in a gust tends to spoil the fun.

Hulls such as the one you are contemplating, with their broad sterns, tend to be more or less severely unbalanced. I wrote a paper on hull balance for the Chesapeake Sailing Yacht Symposium some years ago, PM me if you'd like a copy.

Another design point is to get the LCF slightly aft of the LCB, which appears to help tracking and avoiding diving on the run.

Cheers,

Earl
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