Michael Storer Boat Design 

Hi,

Took the boat out over the weekend and raised the sail for the first time. Ignoring the high wind and the inexperienced crew, I was still very concerned with the instability once on the water, in fact we flipped as soon as we began our first tack and thereafter struggled to right the boat again. I was hoping to get your advice on some of my thoughts.

I believe the instability is increased because I have used heavy gauge aluminium tubing for the spars which has the effect of making the boat very top heavy. I will be testing some extremely light weight spars in the coming weeks (possibly bamboo lug and boom).

I also think that the boat sits very high in the water which may require additional ballast to improve stability. I have three questions regarding the ballast:

1. Does the design call for ballast?

2. What are the best materials for consideration as ballast?

3. What are the best locations for ballast placement?

I was a bit confused at this point as no other GIS has ever needed ballast to sail properly – so there was something strange happening.

I answered the email telling the customer that the weight of the spars is part of the issue, but excessive stiffness of the heavy aluminium tubing has a far worse effect. The wooden spars on the GIS are designed to flex just the right amount in a gust so the boat accelerates smoothly rather than staggers and falls over – just the problem the owner was having.

I also asked if there had been any other changes made.

There is one other thing that I may not have mentioned to date in our correspondence. That is the fact that due to a number of factors such as availability of shed space and availability of ply sheets, I made the decision to reduce the overall length of the boat from 4.7m to 4m. I made this decision in consultation with Mr xxxxxxxx (he gave the name of a well known boatbuilder) about the practicalities and consequences of my actions.

I am certain you would not approve of my decision and in hindsight I would have done things differently but unfortunately things are as they are.

While is is sometimes OK to reduce the length of a powerboat or rowboat and more often OK to increase its length it is highly risky in a sailboat.  This decision had:-

Cut the stability of the boat in proportion to the length reduction – about 15%
Made the original sail area too large for the shorter boat – by around 22%

Put the sail a good old English foot out of position relative to the centreboard making the boat difficult to steer and terminating any chance of good sailing performance.

I suggested strongly at this point that I be given the opportunity to work out some way of making the boat work OK using as many of the existing components as possible.  So I asked for more information about the exact measurements of the sail that was made.

I have attached some dimensions that I have measured off the boat last weekend. Also find attached the amended sail plans as recommended by the sail maker.

The sail area as recommended by the sailmaker was about the same size as the original sail – but the geometry was a bit different. The sailmaker had not attempted to reduce the sail area to suit the shorter boat or attempt to get the sail area in the right place relative to the centreboard. 

The shorter boat only needed around 80 square feet of sail compared to the original 105.

So I took the information from the client worked out that if the sail was reefed at 550mm from the bottom that the centres and area would all work out OK.  So an extra reef point fixes that problem and allows the sail to remain full size if it ever is needed to go onto a bigger boat.

Also I drew up some new timber spars for the boom and yard to restore the missing flexibility and gust response.

The boat will work OK now – the owner has been doing a good job of correcting all the problems.

The rule is – if you want to change the boat – please have a word with the designer first – after all they are the one who understands the boat best. This is doubly true if it is a sailing boat where there are many important inter- relationships.