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Re: Bristol Channel
« Reply #45 on: Oct 21, 2019, 12:30 pm »
No worries Ross, hope your feeling better.

Re: Bristol Channel
« Reply #46 on: Oct 21, 2019, 12:48 pm »
Grass is a real issue for small craft as is vegetation for larger ones !  Due to the low ground pressure, the skirt can't compress the grass and thus there is an air gap under the skirt ..and all your cushion air is lost. 


I would also think you might want to beef up the engine mountings and use box section steel.  If the engine moves and the fan impacts the cowl you will have a catastrophic failure and won't be going anywhere until fixed,  which is a nightmare job away from home. I have several T shirts for that one :-(


Engine sizes also depend where you are going to operate - at Weston you need a lot of spare lift due to surface conditions - if river cruising you may get away with less.  I increased Britannia's lift from 8 to 13 bhp and it transformed the craft.  Not particularly in the way of handling,  but for obstacle crossing, mud gullies and more relaxed operation.




Re: Bristol Channel
« Reply #47 on: Oct 21, 2019, 1:03 pm »
Regarding cowlings, Britannia had the early BBV slotted cowl that was pulling a vacuum with the 13 bhp lift engine, so I cut them out and put a pair of large spray deflector intakes. It was quite a complicated GRP job with lots of compound curves ( hot melt glue and foam core works wonders ! ).  It gave a huge improvement as the intake for lift air is unrestricted.

Re: Bristol Channel
« Reply #48 on: Oct 21, 2019, 1:33 pm »

Quote

   " I would also think you might want to beef up the engine mountings and use box section steel.  If the engine moves and the fan impacts the cowl you will have a catastrophic failure and won't be going anywhere until fixed,  which is a nightmare job away from home. I have several T shirts for that one "

Regarding blades catching cowl, many years ago (about 40!!) I built a Scrad HC out of wood, the "lift cowl" was rigidly secured to the flexibly mounted ( with exhaust bobbins) engine frame. There was about 1.5 inch clearance between the cowl where it went through the deck, the flange of the cowl was sealed with foam to the deck. If I hit an obstacle the whole frame could move slightly without the blades catching!! It seemed to work ok and I could have minimum blade/cowl clearance!

Re: Bristol Channel
« Reply #49 on: Oct 22, 2019, 12:07 am »
That's innovation ! :)