I'm in the process of designing my own merlin-rocket how do I work out where to put the mast and how big and where to put the centreboard?

Have a look at the class rules .

they don't say because it is a development class and all only restricting the boards depth to 1400mm. I Know that the board position is related to the centre of effort of the rig (which depends on mast position) and the mast position is related to the centre of lateral resistance of the underwater stuff (which depends on board position)

rough guide - from a previous forum post

Mast approx 60in back from stem, you should be able to calculate everything else from there.

how much does that vary? any other design issues raised in previous posts?

Would suggest you make a study of current boats,
There are many influencing factors, rig measurements in relation to underwater hull/fin shape. 
Centre of effort(C of E)the rig in relation to Centre of Lateral resistance (CLR) hull/c-board.
There are numerous books articles on this as I'm sure you have found but a good bit of measuring current boats will give you an insight to the basic theory. There are other influencing factors
with the hull shape/buoyancy/lift/drag etc but in effect copying good new boats will cut out to much of the gamble if your not to sure of your ideas.(mesuring old boats is fine, but time marches on!) You could buy a set of plans of existing boats if you just want the challenge of building a boat without the guesswork , good luck Barry.

Try following link, an article by Dave Fowler on deck stepping, gives an actual measurement.

Get in touch with one of the current designers . It doesnt have to be a Merlin  designer ,You will be suprised how helpfull they are at taking the guess work out of measurements ,if you get it wrong its exspensive and the boat will go like a pig .Do you know what works and what doesn't on the water .If you do then fine .If you dont ,then get in touch with the top 5 in the class.Im sure they can help.Talk to the known class builders .They also know what works and what doesn't Southampton Institute!

Good luck
Doo

Doo

what aspect ratio and jib to mainsail size works best in the m/r

...and how tall skinnny / short fat to make the jib?
what wood to use for thwarts, inwales, gunnwales, knees, frames, any thing else not made of plywood?

I have a feeling the name of this design is going to be 'Stream of Consciousness'....

GGGGGGG

If you dont know what size sails to use on a Merlin ,then you certaintly shouldnt be building one.Sounds like yer heads in the clouds and up ya arse.
Doo

I seem to remember one design in the 'book' - edging towards a national 12  the mast further forward in the boat - I think there were one or two comments on the performance as well.

Maybe it is a social experiment to see if you can design something that you know nothing about just by using an internet forum?

If it wins the 'tiller I'll buy one.

I havn't found an appropiate design in the design guide for lightweights (summer wine comes close but is very old and adapting one to have low bow tank deck step modern hull shape etc will always be a bodge job) I know that the upwind sail area is 110square feet but not the BEST way to split it between main and jib high and low, and my sailing club is very shallow so the foils have to be short (i've worked out how wide they need to be as a result). I rekon Mahogany or Teak would be good on the not rotting and ashetic front but are heavy and not very sustainable so thought someone may Know of some miricle speices to use and it will be called 'buisy Beaver' after the club it will be designed for.

Why not look at the Keith Callaghan web site,the boat build has had a lot of air time on Forum over the past few months,Hazardous is for lightweights

good to get some beaver in the Class!

Especially if it's a wet beaver

If your not sure what to use for materials other than for the shell, why not try carbon?

Hopefully not all Hazardous designs were created equal... i'm no lightweight!

Unless you have your heart set on designing your own, in which case Keith Callaghan may still be a good start, I would point you at the link below.

I have been building the Hazardous design for the more bouyancy challenged but he also did a variation for a commission from France which was for a much lighter crew. He charges about 80GBP for plans which are for much more than just the hull-shape. He also provides additional support as you need it.

I have a website showing my construction process but I also have a long list of things I would do differently, but only as far as construction is concerned. The actual design has yet to be proven so don't know if anything would be changed there. Okoume plywood is lightweight [18lbs/sheet of 6mm thick 4'x8'], genuine mahogany is also very light, the prettier mahogany's, like sapelle, are not. Cedar is also very light but not terribly strong without a coat of glass. Then there's CF, not my bag, used it a little but not as much as Miles. 

Happy to give you any help I can, if you need it. We should be in the water in a couple of weeks, the humidity here is holding up the varnish drying time and has set us back a couple more weeks. Very frustrating.

Have fun

John

Our site is: http://home.nycap.rr.com/thekeelings/MerlinRocket1.html

yeah think I need to dith it to do some more reserch first, African Mahogany is lighter than Brazilian are summer wines still competitive and max width (i'll need all that leverage), is much Known about the small Hazororous version

Surely if you made it with Asbestos it would be hazardous?

First starting point, would be to study Merlins local to yourself. See how they are built, and what materials are used. Max beam does not equate optimum hull shape.

One way is test your hull shape design via some computer software [remember to add crew weight for displacement calculations, and assume 120kg or so for all up weight]. 

Or do it all long hand if you're that way inclined [equations available on the internet somewhere].

Calculate total surface area, then the weight of the shell can be calculated( 18kg for 8 X 4  6mm  as John says) weight of glue etc..

You then know what weight is left as a maximum for the rest.

it is being designed around a crew weight of 120kg (19stone) therefore a design displacement of 243kg which as it stands now has a wetted surface area of 4.098 square metres anyone know how this compares to others?

Actually Miles, I was mixing my units and the 6mm sheets of okoume I had were listed as 18lbs not 18kgs. Its the American exPats disease... 1/2 English [as the Muricans call them] and 1/2 metric units.

The French guy, Cedric Burier, who was going to make the Hazardous 140 had not started last time I spoke to him and didn't really think he was going to very soon.

I would think you stand a better chance of getting a pretty competitive boat from Keith vs starting from scratch unless you really understand what makes a good design vs a almost good design! But if you're after the experience then thats a different matter.

There are also plenty of books out there to 'help' you design. None are very simple, because its not a particularly simple process, most are aimed at the big boat market. There is also software for both hull and foil design. Some of it available as shareware or even freeware.

Sail plans/design was not part of the plans package I got from Keith. I guess the development of these has been over many years and includes shape etc which is individual to various sailmakers. It may be worth just working to off the shelf sails and going with whatever is available/best at the time.

Have fun

John

I had a copy of 'Mac Surf' on which I dodled with a design
the main problem is your always playing catchup with existing designs, the 'they have done it before' syndrome
Like so many design solution it so often pays to get hold of a good design and alter it to your ideas,alter what you think needs altering & look / question your resoning.
It's interesting that the current frontrunner the 'CT'has gone through much fine tuning by respectable & sucessive builders. Maybe a design known to be fast of the same era
say the 'Thin Ice' could be tweaked to come in line with lastest thinking. I realise the 'Easy Roller' is a collaberation with Phil Morrison 'Thin Ices' designer, paying £70/£100 for a set of plans is a small price to pay
considering the investment you intend to put into a new toy.