Day 13
Days remaining: 221

Moth Design Considerations 1. Construction.

... but first a quick Boat Update

2 Halves of combined hull and foredeck, joined. 4.8kg

By the time you read this, the mast bulkhead will be laid up and the rear wing half frame and centreboard bulkheads will be in place. We'll be at 5kg,  My target weight for the entire hull, with wing sockets, centreboard case, deck on, painted ready to fit out, is 8kg mainly because my kitchen scales won't read accurately past that ;o)  
Seriously tho, that should easily give me headroom for any hull mods I want to make before I go racing. I think if your hull, fitted out is in the region of 9 or 10kg, and likewise wings 6kg, foils 6kg and rig 8 or 9kg you're pretty much ready to rock with a circa 30-32kg boat. I think now that it has been shown that heavier boat/helm combinations just point blank go faster above say 15knots, and that the whole boat is literally on your side in terms of righting moment, the only advantage to going lighter than 30kg is in the marginal stuff - and with some boats in breeze at 10knots and others lowriding in flat calm at 3 knots, that is a lottery in any case... So I'm happy to add an extra laminate here and a bit more adhesive there and have a much stronger boat, provided I stick to those general weight parameters.

Actually, I want to use some of my diary to open up a discussion about home building of Moths.... and it would make sense to start with construction.

So, with a perfect radio announcer link...

Firstly, build strategy....

Assuming that the first part of a home build Moth is to make a plug and a glass or carbon mould, we're firstly going to jump forward a step to consider what that mould needs to look like, by which I mean, what parts is it going to make.... There are two clear ways ahead... a mould which makes the hull in one piece, to which you add a moulded deck, OR a pair of moulds which produce the sides of the hull and usually the foredeck too at the same time....

With the latter: The foredeck being an integral part of the hull mouldings is cool when making the boat from a pair of symmetrical halves, but you do have a long central seam to join and you then still have to stick the deck down on top of your internals.  Is this seam join more vulnerable than that of around the edge of a stuck down foredeck? Well I really wanted the foredeck to be integral with the shape and add a lot of stiffness (the foredeck is the same carbon on nomex laminate as the rest of the boat) so I went for this arrangement. Joining the two halves together out of the mould proved very easy in the end - using 2" wide wooden batten inside and outside of the hull, screwed together through the join to locate and clamp the halves properly.  I think anyone could manage it really - so it will work well as a kit - which is for me of course the idea eventually.

Traditional, 'Hull + Deck' moulding means of course you can be sure of never having an issue with the two halves coming undone down the middle!  ...and you can mould the bow in one piece too.  This is a big deal with moths as there is a potential for a lot of water pressure at that join on a big deceleration. However, you do need to plant the foredeck down onto the edge of the hull and then get inside to laminate the join unless you have made a rebate in the mould for the joining area.  Not a massive deal, but one to consider. What you do have with this method, is a boat to look at just about straight away - and that means the rest of the build can happen very quickly as it is easy to envisage what you need to do next....

The key 'same stage' point for these two common methods is with all of the internal frames in, and the foredeck on and the deck ready to go down. I wonder sometimes about a single piece moulded hull (very easy to do technically) and I used to think the requirement for internal frames, a mast support and a centreboard structure would make that impossible, but after my short time at Caterham F1 where out of necessity, they make closed moulded structures wherever possible (to reduce process time) I figured out a pretty easy way to get around those issues.... If I had the budget, you can bet your bottom dollar one of my R&D projects would be a single piece moulded hull, bladder moulded in a carbon tool...  Then you could have to option on going super LIGHT (I would say 6kg ready to fit out), or use that 2kg to 'tarmac' down a load more M55J carbon and go MASSIVELY strong... Yeah, like I say... Budget...

At the other end of that budget curve, I've often thought about carving a one off boat from a block of polystyrene and then putting a single skin of carbon or indeed 200g glass over it, just to hold it all in. The issue is the stiffness around the mast and case and gantry mountings (as usual!) It would be fun to pay around with, but I think ultimately the boat would be heavy and not last very long, particularly in the working deck area....

Next time we're looking at boats, we'll jump back and look at that plug/mould making process...

Right now I need to do some stretching and go for a run... but I have to make some orders go out of the door first...

D