I have almost completed my revised drawings of the Pacific Magic. The revisions I have made are in the method of assembling the rear axle tubes to the center spine section and to the steering. The angle of the "Y" remains the same. My questions are :- Is the seat as drawn strong enough to support a weight of 134kg? The seat is highly cantilevered and looks rather insuficient to withstand my weight (bulk). I drew the seat section with extra depth support but the profile looks rather deep at the new depth of 300mm .
Can you please tell me why the frame is "Y" shaped? Does the "Y" design make a huge diference in the performance of the L/Y or does the benefit of the design lie in its ability to be transported with ease and not the least, its asthetics? The swept back axles certainly look wonderful.
The total length of each "Y" axle is 390mm longer than a "T" axle measured from inside the wheel to the center of the spine. Does the extra 390mm contribute to the performance because of flexure of the longer axle? Flexure of the axle is minimal but it is still there. Maximum alowed deflection of a beam is 1/350th of the span if my memory is still active so the flexing is still very little (3mm).
If the "T" style is constructed with swept forward axles then mounting of the seat becomes easy and a much lighter seat can be made , it would also bring the location of the rear wheels to the position shown on your drawings .
Swept forward axles would bring enormous loads to the axle, (same as the wings of the fighter aircraft with swept forward wings) but a lightweight stay from the axle inside the wheel to the spine near the mast area would overcome these loads with ease. I think I saw a photo of a high speed L/Y with swept forward rear axles a long time ago.
There is no weight penalty with an extra 800mm of pipe if a "T" structure is built. The weight remains the same if a conventional "straight "T" is used or if the "Y" style is used. There is some extra weight added if swept forward axles are used. If I had such a design, I would miss lunch, dinner and breakfast and then there's no problem . Yeah, right!
What are your thoughts about these questions? All others reading this feel free to add your comments as well.

Kody

Hi Kody,
I am sure Paul will have some thoughts and answers to your questions. He understands that sort of thing, I don't I am just happy to sail them

Paul is away for a few days. I am sure her will respond when he gets home.
Susan

Hi Paul,
I was 6' 2" but I think I may have lost a 1/2" with the onward march of maturity (ie, age, now 65). I am still relatively agile having had to run down my disobedient shepherd on Farnbourough Beach. Living at Bondoola means that 99.0% of our sailing will be on Farnbourough Beach, running from Bangalee to Sandy Point/Corio Bay. It's only 12 miles but the beach is about 500 meters wide at low tide. My greatest handicap is my weight (cough-cough) at 134kg. I am sure our shepherd will wear that away very quickly (pant-pant-gasp). We hope to take the L/Y to other venues when we can and have a go at racing as well. Any info you can offer will be most appreciated.

Hey Cisco, there are two grass airstrips up here that need to be checked over. One in Yeppoon and one in Emu Park. Might be great places for a sail.

regards
Kody

We live 10k from the beach, about 8 to 10 min drive. Farnbourough is about another 5k, about 6 more mins. We used to live on the beach at Bangalee, we had a love/hate relationship for living on the beach (about 200m away). We were actually very glad to move. (Hey is this bloke crazy!!???)
The major problem we had was the consistant corrosion of all my precison tools and electronic equipment. This also included the fridge and washing machine, my rifles and the list goes on and on. Living where we are now is indeed the very best place to be. There are no traffic jams, no crowds of people, no tobacco smoke, no corrosion from salt air plus we enjoy the wonderful aroma of eucalyptus from the trees and only 10 mins to the beach.
The only transport I have for a L/Y is my 7' x 5' box trailer.
The surface of the beach is almost like smooth sandstone for most of the time. Ask Cisco for comments. It is definitely a beach suitable for high speeds, > 60 or 70 kph. I think the legal speed is only 50kph max but how do you measure the speed of a L/Y?
The prevailing wind direction is E to SE which puts the wind usually at 45 degs to the beach. The average Wind Speed is 15 kns gusting to 20 kns. Many a time the WS has been 20-25 kns and gusting to 30 kns. An Easterly blows at 90 degs to the shoreline. Depending on the time of the year, the wind will blow 24/7. We have been waiting for months for calmer weather so we can go fishing behind the Keppel Islands about 25 klm from the shore,

Kody

KODY
Had thinking cap on and my suggestion to you would be to build a modified MINI
first mod- step up one size in the rear axles, ie from 30x30 to 35x35 then use 40x40x2mm for the rear. Resist the temptation to go to a heavier wall thickness .Dont put as much camber in the wheels. You could have the wheels vertical and have a dropper on the axle to keep the chassis level.
The sail area would be ideal at 4.5m on most days , 5m on a light day.
have your seet slightly further forward (60-70mm). ie feet right forward on the yacht.
one of the first minis we built here is sailed by TEST PILOT 1 with 30x30 axles and he is 6'2" and was119kg at the time.. His personal best speed is 110kmph in that yacht

Hi Lachlan,
The max deflection of a beam is rated as 1/350th of the span. This means that if you had a steel beam, 750mm long, that was suported at each end and loaded in the middle, the maximum amount allowed for the beam to bend (downward) at the middle, would be 2mm. Two mm is equal to 1/350th of the span. ie. 750 divided by 350 equals 2.

I cant remember how the cross-section intergrates into the equation but the equation refers to the safe load that such a beam can suport before reaching an unsafe amount. ie, is liable to failure!
Another way is to imagine a flat bridge, 350 meters long suported only at each end. Max. deflection in the middle would be 1 Meter!. This would not be alowed. For this reason, bridges are built with a curve, higher in the middle. By curving the bridge, the structure comes under compression and is much stronger. It also wont deflect like a flat bridge would.

If your S/Y axle is 1500mm long, I would guesstimate the safe deflection would be a maximum of 4mm. This is a large amount (4mm) and the forces involved would be very high. Unfortunately, I cant remember what the safe limit is for a cantilevered beam (suported at one end only). Reguardless of all else, I wouldn't like to flex such an axle more than 4mm.
However, dont forget, this is the theoretical safe limit. It might take a lot more stress before failure but when it does fail, it would be sudden and spectacular. If you were involved (as driver/pilot), you could become extremely excited, feeling lots of sudden pain.
Stress = strain = high speed = excitement which may = pain = RDF
Hope this helps

Kody

Yes