We don't seem to have many yachties on this Forum but there is a lot of online information about Star 45s such as this site: **LINK**

Just Google Star 45 model yacht and you will get lots of hits.

Colinj

Hi Samuel

I'd estimate 7-8lbs seems average for a 50"Marblehead, the Star is not much shorter but being single chine has a fair beam/displacement. You can take some weight off the lead bulb if she comes out over weight or too deep in the water.

Regards Ray

For the full size model according to the information in the link, it is not the bulb weight at minimum 12 pounds, that is the entire boat including the keel weight where 12 pounds is the minimum sailing weight. Since your model is about half the length, and when talking weight you are also talking volume, thats about 1/8th the weight. With a ballast ratio of about 50% you are in the 24 oz area total, so a keel weight of about 12oz, maybe 14oz. This fits well with the old Akela design (used to be a free plan years ago) that was 25" long and carried a 12oz weight as well as the modern 25 inch racers (DF65) which carry the same weight.

Shrunken yachts rarely perform up to expectations without there being some modification, usually a longer fin with the same weight to enable sailing in a wider range of conditions. The bulb does need to be a very good hydrodynamic shape, casual lumps cripple performance.

Just looked at my Victoria. Its 30" long, weighs 5 lb and almost half that weight is the bulb. The draught is about 9" (waterline to bottom of weight, and it carries 400 square inches of sail on a 39" mast. While by no means the same boat, yours is somewhere between that and the old 25" Akela , now known as "XL25" with drawings and more information at http://www.sealevel.demon.nl/english/downloadsXL25modelyacht.htm

Hello Samuel
​Lots of good information coming your way particularly around the scaling effect that does not work in your favour. Malcolm was certainly pointing you in the right direction and I am sure he won't mind me pointing out that when he described making the keel longer he really meant deeper. On a yacht, long keel has a meaning of its own and the important thing is to get the keel weight (and therefore the centre of gravity) as deep as possible.
​As to the weight required on your model it is very easy to find out by practical testing in a bath. On the plan it will show the designed waterline and you can mark this on the hull. You now add weight making an allowance for mast, sails, fittings, radio, batteries etc and when the model is floating on that waterline you can measure the added weight and that is the amount of lead you have to add to the keel. The link from Telstar is a very useful way of getting the dimensions of a bulb shape that is the weight you want. Lead is not very strong so although a narrow shape creates less drag it will get bent easily if it overhangs the keel. A model yacht for just pottering about will be fine with something a bit stubbier.
​Finally and due to the scale effect and not having to comply with any rule I would keep the depth of the keel only a bit less than the original and not in proportion. Remember, the wind doesn't know what size the boat is.
​As to ways of casting the lead you will find lots of ideas (and precautions) on U Tube.

Hi Ray, what sort of keel weight do you have on your Thames sailing barge ? The barge I've recently built has a 3kg bulb weight but I'm thinking its not enough should the wind pickup, its a 1:24th scale. Also whats the depth of your fin/keel ? I took it for its first run the other day and was a bit disappointed on its performance, Most probably due to the lack of wind, 11klm/hr.

Regards, Andy

Hi Ray

So i`m probably not too far from the correct weight of 3kg, the allup weight of my barge is 9.7kg the fin is a traditional keel shape with depth of 9-1/2" so I'm not too far from the right depth, Your winged keel looks interesting. My barge is scratch built and a lot of guessing from photo`s of other barges plus. More trials underway hopefully next week when the winds are more favourable.I liked your H.M.S. Diamond model, an old ship of mine.

Regards, Andy