35' cat concept for the inside passage.

I'm confused. What surface is doing the slamming ?

 

With internal engines the minimum width is defined by the engine room space you NEED as opposed to "Like" ... I like a sail-drive because it is an easy and neat installation with minimal through-hull-holes... but that is my choice, yours may well be divergent/different...

Match the above performance figures to my boat using 21hp motors, delivers 10+knots at 6 litres/hour (both running)...

Aft berth is super large and could be lowered about 12 inches (to the chine for the "45-degree-chamfer") for standard double bed width and comfortable sitting space... See image... 2286 (looking aft from laundry - stbd hull) and 2301 looking to port before deck and bottom of berth put in place)... 2305 shows the flat bottom from aft of stbd hull, before transom and other bulkheads are fitted...

 

ya after countless changes back and forth I got lost in there somewhere, my bad, Ok I'll sketch up something new and post it soon as I get a chance. I'm supposed to be going out tonight but our plans are kinda tentative. I suppose I should make a phone call, Damn I'm getting old, at one time I'd be bouncing off the walls trying to pin one. Oh well, apathy does seem to work kids.


OK so the hulls presented in post 432 are about 1066mm wide, which nobody liked. As thin as I can make them is about your 840mm mentioned earlier. I have a sketch with the rocker bottoms and the narrow hulls around here somewhere

found it
this ones got the hulls at about 40" wide or 1000mm and I'd like to get em skinnier, something like 32 or about 800mm


But I am really interested in what Richards got to say about the at rest characteristics of this hull form, and I also was not clear if the slamming mentioned would occur under the bridge deck or bottom of hulls. Either one is not particularly acceptable. I'm OK with a little slam underway of the hulls but not the bridge deck. I've varied its clearance from 32" to 36" in the different drawings but I'm really trying to provide more than enough clearance for any reasonable scenario this boat might see either on the inside passage or making any sensible crossing to Hawaii

And Mass, good point, having always turned my own wrenches having a little room to work on the mechanical is definitely a consideration

PS
Groper, it was painful to see that old sketch it was so bad. Damn you guys must be laughing your asses off at me sometimes.

 

Mine bumps occasionally when at anchor in a tidal current (at South Percy Island sheltering from a southerly blowing up to 40 knots) that produces short-steep waves coming in the opposite direction - occasionally producing a nasty surprise... for a "rude awakening".......... as it falls off a wave passing forward and the aft section lands vigorously.... otherwise nothing ???

To give you an idea of the underwater hull form and general presentation.... waterline is about 2 inches below 'anti-foul' at stern (about the line of the second chine join) and 10 inches below anti-foul-paint at bow (in the profile view - about where the shrub/lawn line is behind the bow)....

 

It's the waves doing the slamming. Imagine being in a cross sea. The waves hit the side of the boat and have nowhere to go.

That's why I like a knuckle, even a small one helps, and why I draw gently Veed bottoms to my bridgedecks rather than have them flat (ie horizontal)

An extreme case is this Lion 46 from the Moorings fleet. I remember reading a review by a charterer who said he couldn't sleep at night because of the waves surging through the bridgedeck

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

the Moorings fleet eh, lmao.

 

No slamming of waves on my bridge-deck undersides - yet.....

The "lion 46" looks like a split mono and a couple of ft extra beam - To what effect ? or purpose ? To go like the clappers ? with HUGE power-plants, and a harsh enough ride to rupture anyone's bowels if afflicted with "piles".... and 6 inches of bridge-deck clearance? - - - HOW SAD.....

 

Bos, 840mm waterline beam is quite narrow, which is why i was encouraging you to angle the topsides, or add a knuckle etc to gain more volume inside ABOVE the waterline...this was way back in the first few pages of this thread... youll need to be very clever about this if you are to create a design that has a narrow waterline beam but still enough space in the hull to work on a diesel engine for example... You wanted to maranize a 300D engine, i have no idea how big these are - including how you package the ancillary stuff attached to it... One good thing about a purpose bought modern marine diesel, is that most are designed with packaging well thought out and can be fitted into some pretty tight spaces... With everything your trying to do in your 'concept' your really pushing **** uphill to get it all to work together im afraid... multihulls are not easy in this respect...

Heres a diagram of the nanni N4.38 (38hp) marine diesel engine, its narrower than both the 30 and 20hp models; Nanni`s are cheap, no frills reliable engines... might suit you?

 

Spare parts are easy too as it is based on the small "lifestyle 10 acre lot" requirements tractor from Kubota... - the Nannni marinisation has several useful mods like a sump pump for oil changes and a few other nice marinisation bits... and a neat wiling loom - plug and play with several console options... the OEM package is the jewel in the crown...

 

well I haven't chosen an engine yet, I prefer to be more of an opportunistic feeder if you know what I mean. But if I've gotta chose something ahead of time and then go searching it out then its going to be something extremely popular that's able to convert to alternative fuels. I've absolutely no intention of paying the exorbitant fuel fees at the dock. IDI, naturally aspirated, mechanical IP. I'd use another 7.3 if I thought I could get away with sticking a 1/2 ton chunk of cast iron in this thing but something tells me thats just a tad to heavy. I think the Merc300D engine weighs in at about 500lbs so its the more likely choice. I'll figure out oil changes and modifications as necessary but something tells me I could make it work no worries. Its pretty much just a mater of weight. VW made a pretty good diesel for there Rabbits a while back, I should look into those as well. Marine engines are way pricey and I'm going V drive to take the thrust off the engine so I was thinking I'd be able to get away with an slightly over-sized terrestrial diesel. That 300D engine is ~80hp and very reliable.

If I did the commuter I'd use the 7.3 or maybe a pair of them. But I'd expect to get at least twice the mileage out of a cat. Which is a major consideration in my book. I won't get the luxury I'd get out of the commuter, but half the costs is very appealing.

 

300D engine weighs 570 pounds dry,can't remember if the turbo was on or not-in any case would add 20 pounds or so. Call it 600.

Cummins 3.9 is 740.


But if it were me I'd import a couple Toyota Landcruiser engines from Japan...they're used by Yanmar. 105 hp 6 cylinder or the 4 cylinder 90 hp.
If you can't do that in the US due to EPA,we have them in Canada.

Let me know I can price them.

 

there's a couple of them I think they range from 2.0L to 3.0L with a millage difference of about 10mpg between them. I'd likely go with the 2.5, if I remember its the middle of the road one thats most common. Hmmmmmm wonder what it weighs VS what the land rover engine weighs. Still 600lbs is a long way from the 950+ the 7.3 weighs

Hmmmmmm snowing out and I'm out of beer, not acceptable, brb

 

And the VW Marine (now part of Cummins Mercruiser) 2.5 litre 5 cylinder is 255 lb, for 96HP @2600rpm. (Edit: that's 225 kg, sorry!)

The one thing I've noticed about Cat owners is that they become absolutely anal about weight. They get very selective about the 'stuff' that comes aboard. Something about performance, and separating cats from dogs. Of course some people prefer comfort to performance.

With Groper's skinny hulls, less weight, less fuel required the design spiral is heading in the right direction.....

 

lmao cats and dogs eh, well The new dog is going to have something to say about that.

Gotta look up that VW.

the Mercedes I'm still looking into, but its this one
OM602.961 - 2.5l inline-5 turbocharged, 123hp, used in 1987.
although I might forgo the turbo if it turned out to be a pain in the ***. Although in Alaska the extra heat might just come in handy.

hmmmm no luck on what that Merc weighs but I'm pretty sure its not under 255 lbs. Hell it'd be a miracle if it was under 450 lbs

 

Holly Smokes you forgot to list the price.

not happening at 40k or even at 1/4 of that, I can get a 602 for next to nothing ( a runner for under $500 easy) and rebuild it myself, gives me a chance to get to know the engine a little. Damn that was a shocker.

Ya I appreciate the thought though, phew, lucky I was sitting down and with a beer handy

YIKES

Carefully put that back on the shelf and slowly step away

did I mention cost effectiveness yet ?

besides I might need some led forward if my hull really turns out to be that far out of balance. Which is something else I've been looking at. Just as a preliminary I'm seeing my hulls are forward heavy buy a fairly large percentage. Should offset my deck structure being off aft or at least make up for a healthy percentage of it