35' cat concept for the inside passage.

The rest of that I didn't even bother to read because obviously your off on your own agenda here. I think its becoming obvious who's not listening

 

You do realise that the example given is a SAILING cat that would have capsized due to sail load.

What you propose to build is a POWER cat.
They have no mast and sails so your capsize example is irrelevant

 

Ya thats a big issue in my book. Pretty much universally fire is agreed to be the bigger concern. My thinking on that, once I get to that stage is to use a fire proof enclosure of the engine room and a fire suppressant system, Keep all the fuel well away from possible ignition sources. Thats way down the road tho. Gotta run new preliminary weight calculations on the new forward profile. See if I added any more plywood or not. It looks like by shrinking the width of the bridge deck I gained some structural integrity in span. Richard mentioned that earlier but I was thinking a narrower hull form would go through the water better. Not sure as hull forms are bound to be my worst thing as I don't have any modeling programs available to me.

Oh well still working on it

 

alright lets get back on track



The change to the hulls was to widen them from 2.5' to 3.5' to add multiple chines and to put a rocker on the bottom. Basically loose my Bolger hull forms. No idea how that effects performance but it reduced draft ~4 inches. It also means I have a lot more reserve buoyancy and I've got a less abrupt face going beam on in case I end up needing to slide sideways away from something.

each hull went from gaining ~466.7 lbs of buoyancy per inch submersed beyond the chine to gaining ~653 lbs pr inch submerged past the chine. It goes up a little because of the flair with each additional inch but its a pretty substantial gain in buoyancy

Thing is someone said make the hulls thinner and deeper and then someone said make them fatter. Its kinda a nightmare tying to incorporate so much conflicting information. I'm using Richards suggested 3/8 average ply thickness and doubling the total ply used to get my weight estimates for the finished shell.

Once I know if I'm in the weight range I need then I can continue, now that I've got a forward view that looks something like a cat that is.

 

Guys, let's try to keep the forum threads civil please.

< Some posts which contained insults directed at another member have been removed to clean the thread up >

 

thanks, feel free to remove any with religious statements as well.

 

thanks

Ok so I got 175 sheets with about 25~30% cut off, I'm going to calculate two weights one using a BS 1088 in Okoume A/B and the other in Douglas A/B marine ply.

using data from this site. http://www.boulterplywood.com/MarinePlywood_4.htm

I came out with an average thickness of about 3/8 per sheet . As suggested

In Okoume its 28 lbs pr average sheet/thickness

In Dougy its 33 lbs pr average sheet/thickness

I'm estimating 175 sheets for the new design and call it 25% drop offs for two totals of 3,675 lbs in Okoume and 4,331 lbs in Dougy. My cut offs are if anything estimated low but I'll go with 25% for now.

thats also 4200 sq ft of say 6 oz ( anyone know what weight fiberglass cloth I should consider rapping this thing in. ) fiberglass cloth 6 oz cloth takes 6 oz resin so 12 oz pr ft. = another 350 lbs of fiberglass

ends up my shell weighs something like 4,025 in Okoume or 4,681 in Dougy.
now to go find out what a few comparable sized cats weigh in at, but one of our more polite posters mentioned 6 tons as a target weight so I'm in the ball park. I think.

 

When considering fire safety most of the fires ive witnessed were not concerned with the power plant, they were electrical. Use correct electrical engineering practice and top quality materials for the electrical installation.

 

4oz cloth YIKES ! thats nothing. I dont know what multihul scantlings are but Id guess 12oz biax with additional cloth on the bottom and sheer.

 

Ive been a general contractor for quite a while. Always ran my own electrical, never had even the slightest issue. Also rewired my share of RV's, so I'm also familiar with the difference between home and RV wiring. Once I get to wiring I'll go nuts learning what the requirements are for a yacht and making sure I meet or exceed them in all regards. I have no issues at all with spending whatever it takes on say ISO cable or whatever is the premium wire. I used all ISO in all of the trailers or RV's I did. Even build a really nice camper once. All crimp connects and UL listed waterproof everything. Not sure that applies to a boat but again, getting ahead the game.

hows 6 oz cloth as a plywood wrap ? adequate ?

 

It was a wild guess Michael, I'll recalculate for the thicker cloth

= 5,031 lbs or 4,375 lbs depends on what wood I use. Real question is hows those shell weights looking, the weight I'm about to go find are going to be all up dry weight not shell weight. Kinda makes it a pain in the *** to know if I should start trimming or if I can move forward.

 

i agree with the changes you have made to the hull form boston, you now have a hull that suits the speed regime in which you will operate and will carry the weight better. This is because you reduced the length/beam ratio to around 10:1 whilst adding rocker to suit a moderate cruising speed instead of deeply immersed transoms. The problem you now have is youve reduced the bouyancy in the stern, on what already looks like a stern heavy boat... think carefully about this, can you calculate you center of buoyancy? If not, download a program called "FreeShip" Version 3.2... its free, its easy to learn, and will make all the buoyancy and displacement calculations so much easier for you. Once you learn to use it more thoroughly, it will calculate the center of gravity and the mass of every panel in the boat so you dont have to make rough estimations based on how much wastage you think youll have. It will tell you surface areas etc. If you need to make a change to the scantlings, you update the material properties and it recalculates everything automatically. You NEED THIS TOOL, or you wont be successful in your design unless its by sheer luck... You need to get the hydrostatic calculations much more accurate than you are currently doing.

 

here -- http://www.softpedia.com/progDownload/Freeship-Plus-Download-85929.html

 

Hmmmm well the hull form was always going to be my most difficult aspect of the design. Which is why I was so hell bent on going with the Bolger form, its mind bending simple. I can calculate the center of buoyancy, not to hard now that I've got symmetrical hull forms again. The center of mass is a bit more tedious and if that program doesn't run on a MAC its not going to be much help. I'll go see if I can't find it and maybe run it on flip for MAC but its questionable. I'm on a really old computer, works like a charm, but doesn't run some of the more modern stuff.

What I'd really like is a graphics program that might run on this thing. Not cheap when you dealing with a MAC. Oh well.

I'm sure I can cure any stern heavy issues I might have with my trusty eraser, its just that I'd prefer to simply modify the tapir of the hulls aft, won't know quite what that entails until I figure out if my ~5,000lb shell is to heavy or not. Then I can move on to more finely tune things.

One thing that I'm kinda curious about is why everyone is so concerned with the shell balance, its going to be getting a bunch of mechanical all of which could be used to balance any discrepancies in the hulls weight distribution. I 'd rather go with a single engine but might be constrained to have two. Either way they make great ballast do they not? As well as generator, refrigerator, freezer, all the obnoxiously heavy stuff I would think could be wiggled around till it floats straight. No?

 

says its loading but didn't distinguish between MAC and PC which means its not likely to work out to well. Oh well lets see what happens.

No go
its not even pretending to download, just sits and spins, oh well thanks for the effort.

ok I seem to have made something happen, I got a zip file, now to see if its MAC compatible

nope unrecognizable file format = doesn't run on a MAC

it was a good try tho