Hi Roger,

did you think about possibly using a split junk rig as per Slieve's designs? With Footprints having a Fantail shaped sail with Arnie's barrel shape it would be very interesting to compare rigs on identical hulls.

Just a thought.

David

Thank you Ketil for your comments too. There is CF spar manufacturer in Auckland but they seem to specialise in Spars for Arab Dhows. Annie thought they might be for racing Dhows and no doubt those people have enough to pay for CF. Their mandrel is 12 meters long at 250mm OD, tapering to 150mm OD in the upper 4 meters. They would make it 8mm thick at the partners and narrowing to 3.5mm at the mast head. Total weight 70KG...a considerable weight saving considering the original mast was 300kg. Having taken 3 meters off the original mast it now weighs about 260kg!

I don't know how to calculate the effect of shifting the mast forward by 1 meter and reducing the weight from 260kg to 70 kg. Apparently aluminum will weigh twice as much as CF in order to have the same strength. In theory an aluminum mast for Shoestring would weigh 140kg.

Thank you  Arne, those are useful formulas. It helps avoid the guessing game!

The real advantage With a carbonfibre mast is that you can have it designed and Taylor made for Your purpose. The designer would need to know where the bending forces are working, a fair guesstimate of how much, and last but not least, weather the mast is built professionally or amateur. He will then specify the material, how much and in wich way the layers are to be laid. If one could ask a tree to do the same.... 

Footprints has now got a successful rig, but Shoestring still wants to play!

I think the Underwood 32 is a versatile boat allowing for many different sail designs, some of which are Junk rig. I have uploaded three different Junk rig drawings  in Illustrations. Two of the proposed rigs are in a tabernacle with carbon fibre mast. In these drawing I have set the mast in front of the forward bulkhead, but my biggest concerns are

a) cost of the mast (probably unavoidable)

b) Weight displacement. This could be adjusted with ballast but there is a chance with such a light mast the boat can become too stiff.

c) Is carbon fibre as strong as what people say it is? What type of carbon fibre is best?

In the last drawing I propose a Dhow type junk sail with 10 meter giant bamboo battens and comparatively short luff. The lower panel can be reefed up. This would be another experiment using weed mat sails. My gut feeling tells me that the three panels above where I have drawn the boom would be enough sail for 25 to 30 knots wind.

I look forward to feedback.

Best wishes

Roger

Thanks

Roger