masalai's model movie

Sorry Frosty I was cooking dinner for mum. In the image of the hull with the screw removed at the curve between bottom and side underwater.?? Along the side of the hull.

 

What is "the vacuum break"? something to stop the propellor from sucking itself off?

 

Hi Danish, Forever cheekey, only way to ask your views? Have you seen the video & images? Location is in my first post in this thread.

 

eh... "scale" in the search button returns too many threads
"scale calculation" 350 reply's to the seaworthines thread, ough
you may got this allready but here in short what i'm reading
Ranchi Otto recently also explained it very well, but where....
its of great use in design and correct me if i'm wrong here plz

relationship between scaled model and full size

ofcourse linear dimensions only use the scale
areas be reduced by the square root of the scale
volumes and weights be reduced by the cube

all velocity's be scaled by the square root of scaling factor

 

Yipster,
In that case my 4.2knots on the model test equals?
square root of 10 = 3.16 approx so does that convert to 13.28knots?

 

witch i think is an admirable velocity
what size is model the model again?

 

1.2m length w/l for a 12m full size length Water Line

 

This is also one of the boats that inspired my project. Engines too big, and to survey which is above my needs. It has been driven to Vanuatu (from Brisbane) and is now back home & for sale!

http://www.sunshineboatsales.com.au/ed.php?de=31696&range=power_lge

Schionning design 60 pax charter ferry at A$890,000.00 and 3L/nm @ 18knots. max 25knots is nice.

 

you do away with displacement boats sometimes anoying slow speed
that Schionning is 3.5 meter longer thus faster, yours can still be tuned a bit
its what you want, 50 knots is nice too, but hey

 

Thanks Yipster, Prime factor is sub 1L/nm at around 12 to 15knots cruise in flat seas calm winds, with 20knots max is enough if that need to run arises.

 

Masalai if your designing a boat from scratch your very brave. Even big boat manufacturers hate this bit. A lot of money can be wasted especially with high speed hulls. Designing a new displacement is relatively easy and you will get it to work somehow. Semi displacement or planing is a different thing.

In catamaran form it twice as difficult.

My semi displacement cat is easy at 17KTS, wake as straight as an arrow and I can walk away from the helm. At 23 she is a two hands on the wheel job . Like driving a go cart down an icy road. Basically I am exeeding the hulls speed. My only way over this is hydrofoils, or get the bows up somewhow, but that tomorrows job.

 

Yes frosty, I only look stupid? I intend to make sure I have all the information to give a NA/NE to draw what I want up and have it built. Nothing off-the-shelf met all my needs/wants - some wants need pruning, that's the process I'm following and I need visual and physical means to fully understand things I technically don't. Particularly the engineering side - strengths in material and construction methods relative to the marine design processes.

My reliance on this forum is considerable, as I need enough information to identify new or unusual aspects like, is it feasible to mount your system with the thrust bearing giving the load to the transom & other internal bracing so the engine & gearbox can be mounted further forward, linked by shaft & 2 CV joints, to the surface-drive device assembly. This would, for one, make engine replacement easy in the "backwoods" where alignment skills are non-existent, and put weight nearer midships.

 

Your boat looks to have a very narrow rear end meaning your engines will be up under someones bed. Most displacements are like that. Mine are not.

My prop is approx 16 inches off the transom but the shaft is 4 feet and is 21/2 inch this gives me comfort in that the 14 inches is not flapping about. Although the stern tube /log covers 12 inches of it with an extra long Cutlass bearing. If you put a thrust at the transom where is your stiffness, unless its supported externally, then your back to parasitic drag.

My stern tube / log also travels into the boat by another 8 inches and through a dummy transom. This gives the whole thing strength and would not be damaged by the boat settling on them if I wanted to beach.

 

Yes Frosty, I meant near where the shaft ends (inside) so I guess shaft would be somewhere in the vicinity of 4 plus feet long with a lengthy stern tube?, engine is midships mostly down in the "narrow bit" - I have been talking of the probability of widening to accommodate wider engines. Nani 5 cylinder will fit narrow many others won't.

If there were bulkheads to mount the forward end and take the load of the thrust???? Me no savvy, I am not that engineering genius, that you seem to be.

I am trying to illustrate the stern area so I can have an image available for some to assess, decry as ****, or suggest alternatives.

Only 2 beds forward - across bridgedeck, aft is shower, then engine room.... else hammock in "verandah" aft.

 

But your sterns are narrowing to almost nothing and the bottom also comes up to meet the water line? almost canoe stern? This config may work with the very very long Thai boats called 'long tails'. These shaft are 10 feet plus.

Im not one of these guys that produce stuff with a computer, I kneel down and look at it with my head cocked and one eye open and then think about for a week.