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Old 30-05-2007, 19:39   #46
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Dont have a problem with the firehose if it is on a fast boat like the Outremer 50.

You could always slow her up to 12-14 knot's like said earlier and stay drier, and by the look of the bow's you could foam up a "clipper "??? style bow easy enough which would help reduce spray even more.

Id also say that in the "Indigo" clip, she is sailing a fair bit slower than the outremer as well.

She's having a blast though

Nice bit of vid.

Dave
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Old 31-05-2007, 05:41   #47
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Quote:
Originally Posted by Lodesman
Tnflakbait,

The windage might be greater with an A-frame, but that can be minimized by making them a thin aerofoil-shape. There are the benefits of less weight aloft, and no compression load in the centre of the bridgedeck. You might want to revisit Brian Eiland's comments on the effective loss of sail area when it's located behind a big stick (even a rotating mast).

Kevin
I agree with Kevin that the windage may be greater and that it can be minimised by making it an aerofoil shape. The other advantage is that the sections can be made smaller as the loads will be split down the two. Less rigging will also be involved i would have thought. The other advantage the A frame mast is it give's you somewhere secure to stand and view reef's when try to navigate them.

An A section mast would also allow the mast to be lowered a small amount to go under a bridge I would have thought. If you make it so the base of the masts can pivot. If set up correctly it might even be possible to lower and raise the mast completly. No issues with stopping the mast swaying from side to side with an A frame.

I really think I will go with an A-frame mast. An A-frame mast is far simpler than a Rotating mast as well. The rotating mast will still cause turbulence that will effect the performance.
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Old 31-05-2007, 13:58   #48
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?????? a frame

Hey,

What about upwind preformance with an a-frame?? Personally, I'm intrigued by the idea and it looks pretty cool, IMO.
As for the forward cockpit ??... I believe the benefit would derive from a small "workpit" as dicussed earlier for safety reasons when working at the mast... main cockpit should still be aft.
Perhaps this is another adv. of the a frame. I like the idea...even if upwind performance might be slightly affected (it looks like it might to me), who cares ?
Just my 2 cents...

MM
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Old 31-05-2007, 15:59   #49
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pirate Robots

I have only had one encounter with an A-Frame cat. This is perhaps why I don't like it. It was a crappy old Wharram and was really a over loaded
peice of junk. The masts fell down a few times. I'm sure this was because of a poor rigging job.

The main advantage of the A-frame to me is making full roller furling more affordable. Using a furling jib system for the main, and a furling jib up forward.
It does use minimal rigging however the forces on the boat will still be extreme.

To be honest I don't like the way it looks. Aesthetics are very important to me.

Maybe it can be done and look good. You might as well design the masts in that cad 3-d program you did the hull shapes in.



This is an interesting mast:
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Old 31-05-2007, 16:53   #50
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For what it's worth, probly not much, I've got a buddy who skippers one of those 'lectric drive Lagoons and he HATES IT!!! There's all that conversion inefficiency, PLUS you immediately lose the advantage of two engine redundancy (sp?) due to reliance on a single generator. I just don't think the technology is there yet.
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Old 31-05-2007, 20:01   #51
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Quote:
Originally Posted by Tnflakbait
I have only had one encounter with an A-Frame cat. This is perhaps why I don't like it. It was a crappy old Wharram and was really a over loaded
peice of junk. The masts fell down a few times. I'm sure this was because of a poor rigging job.
Don't Wharram's use (for lack of a better term) flexible joints between the cross-beams and the hulls? If both hulls were moving independently, it's no wonder the A-frame didn't work.
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Old 01-06-2007, 02:11   #52
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I like the look of the A frame mast on the SMG-Multihull, it doesn't look conventional so to begin with it might not appeal aesthically but to me it does.

Most Wharram's do use a flexible joint for the cross beams so this would effect the way the A frame works.

An electric motor is far more efficeint than a diesel motor is, and unless a diesel engined boat is running at the optimum speed that the propulsion system was designed for it will be working inefficiently. Where as a diesel generator runs at the optimum speed all the time.

You don't lose the advantage of redundency as you still have the battery backup which will run for long enough for you to either repair the generator or to hoist a sail. At least with a electric motor you are not relying on one resource to provide your needs for motion. A diesel motor will only run if diesel is available, and then it relies on the fuel filters not becoming clogged.

Why will the forces on the boat be extreme, The forces will be the same. The only difference being that the Force of the mast on the cross beam will not be on the beam and won't be a concentrated force, instead it will be a force on the hulls and will be split between the two legs.

A quick question, is their a rule for working out the power requirements for the engines on a catamaran.
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Old 01-06-2007, 02:58   #53
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I'd steer clear of an A frame rig, and i'd have to say resale would be affected.

The rotating wing as in the vid would be my choice on a performance boat and here is an Australian cat that has cruised the world succesfully with a pre bent carbon fibre foam sandwich wing mast.

RICH Challenge newsflash reports

The pic is of a Kiwi cat with pre bent carbon rotater.

As a longevity thing, if doing a remote cruise, I would go for a rig that was conventional and bulletproof, that at worst might lose the top 10 ft, but not the whole rig.

Saying that though, when a rotating rig goes it is usualy one of the 3 wires holding it up that let's go, so you should get the mast and spreaders back on board intact.

Id also stick with a more conventional propulsion system.

While the hybrid electic may be good, electricity and water don't mix, and i'd doubt you'll get a repair done in most places.

If you decide to do an A frame, i'd make sure your mast BH and boat still had the facility to use a normal rig at a later stage if required.

After all, if A frame's were the go, we would have seen more of them by now i'd think.

Dave
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Old 01-06-2007, 03:30   #54
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No offence but not back to re-sale value. Re-sale value is unimportant with this boat.

The boat is a cruising boat not a race boat.

I doubt you'd get a repair done on a rotating mast in alot of places too. A frame masts are in an early stage and I'm sure each type of mast has its own advantages. The A-frame mast for me offers more than the conventional so I will go with it.

Electric propulsion should require far less maintenance on it than a diesel equivalent. Their is far less to go wrong with a electric system than a mechanical diesel. With the advancement of modern diesels and all the electrics involved I'm sure there's alot of places that wouldn't be able to repair a newly installed engine.

Isn't the whole point of a boat to float on top of the water. If the water gets to the electrics I think a diesel would also have stopped working due to the engine having water in it. Also if electric and water don't mix I take it your not fitting any electrics to your boat, including an engine with any electrical components.
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Old 01-06-2007, 03:55   #55
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Quote:
Originally Posted by Steven Prince
Their is far less to go wrong with a electric system than a mechanical diesel. With the advancement of modern diesels and all the electrics involved I'm sure there's alot of places that wouldn't be able to repair a newly installed engine.

.
How do you figure this? If an electric system has a diesel generator to run it then you have all the same potential for problems a diesel has, PLUS all the possible problems electric motors can have.

Also, low power output marine diesels like the ones we use on sail boats have very little electronics involved. They still use mechanical injector pumps etc - really the only electrics are the generator and starter - pretty much like always.

I have investigated electric/hybrid drive for my boat, but as things stand just now, there just isn't a valid case for it. The cost is so much higher that you would need to motor huge distances to recover it in fuel savings. Realistically boats don't do that kind of mileage, even circumnavigators.
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Old 01-06-2007, 04:13   #56
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Quote:
Originally Posted by Tnflakbait
I agree that the plumb bows make it worse for spray. My boats hulls are far from plumb and love to spit water. (In certain conditions) Cats are often very dry. Just like Indigo is in this video. Nice boat!

More Youtube fun:
Aita Pe'a Pe'a

What's more important than the angle of the bow, is the location of the centre of lift of the hull. Many cats have it too far aft, and at speed the bows are depressed, generating spray. If the centre of lift is far enough forward the boat will tend to lift it's bows at high speeds, and generate little or no spray. There's a video here that illustrates it :

GUNBOAT Click on "Video" .

This boat is sailing very fast, and generating very little spray, even though it has perfectly plumb bows. Bows with a fine entry also reduce spray, compared to bluff bows.
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Old 01-06-2007, 05:10   #57
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Originally Posted by 44'cruisingcat
How do you figure this? If an electric system has a diesel generator to run it then you have all the same potential for problems a diesel has, PLUS all the possible problems electric motors can have.

Also, low power output marine diesels like the ones we use on sail boats have very little electronics involved. They still use mechanical injector pumps etc - really the only electrics are the generator and starter - pretty much like always.
The diesel generator is only there for when the batteries run to low. Even if you douse the generator if it does packup you've got the batteries as a backup. Most cruising boats carry a generator aswell as having diesels meaning there are 3 things to go wrong. Those that don't carry generators run the engines under only a limited load to recharge the batteries, which we all now is not very good for a diesel engine. A generator runs at the optimum speed for economy and engine life.

The power output doesn't really mater whether it is electronically controlled or not. If the engine has a CPU which I believe nearly all diesel engines do now then it will have a host of electronics to go wrong. Still need the startor though don't you, I'm sure not many can be hand cranked now.

Even if you don't need electronics for the engine I'm sure most of you all have Electronic nav. They all seem to run ok in a boat, and they use electric.
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Old 01-06-2007, 05:55   #58
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Quote:
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The diesel generator is only there for when the batteries run to low. Even if you douse the generator if it does packup you've got the batteries as a backup. Most cruising boats carry a generator aswell as having diesels meaning there are 3 things to go wrong. Those that don't carry generators run the engines under only a limited load to recharge the batteries, which we all now is not very good for a diesel engine. A generator runs at the optimum speed for economy and engine life.

The power output doesn't really mater whether it is electronically controlled or not. If the engine has a CPU which I believe nearly all diesel engines do now then it will have a host of electronics to go wrong. Still need the startor though don't you, I'm sure not many can be hand cranked now.

Even if you don't need electronics for the engine I'm sure most of you all have Electronic nav. They all seem to run ok in a boat, and they use electric.

Gee, out of every 10 boat's that I know cruising, maybe 1 has a genny, most have solar and wind.

If they have a genny it is a throwaway Yum-Cha 4 stroke for $1000.

I have deliberatetly brought engines for my powercat WITHOUT electronic's to go wrong. No turbo either. Just slow spinning, reliable grunt.

As I said earlier, electronic's and electric motor's won't get fixed at Tanna , or Honiara and they certainly won't get fixed at Noumea and that is where you'll need the reliable, simple system that you can fix yourself with a hammer, WD40 and a rusty shifting spanner.

And how long are those batteries going to last if you spit the rig and punch a hole in the boat and swim the motor ?

Enough to get you anywhere?

At least twin diesel/twin outboard has redundancy built in.

Electronic nav ?, yeah, I carry 2 handhelds and paper on every trip, again, redundancy.

Dave.
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Old 01-06-2007, 06:12   #59
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Quote:
Originally Posted by Steven Prince
No offence but not back to re-sale value. Re-sale value is unimportant with this boat.

The boat is a cruising boat not a race boat.

I doubt you'd get a repair done on a rotating mast in alot of places too. A frame masts are in an early stage and I'm sure each type of mast has its own advantages. The A-frame mast for me offers more than the conventional so I will go with it.

Electric propulsion should require far less maintenance on it than a diesel equivalent. Their is far less to go wrong with a electric system than a mechanical diesel. With the advancement of modern diesels and all the electrics involved I'm sure there's alot of places that wouldn't be able to repair a newly installed engine.

Isn't the whole point of a boat to float on top of the water. If the water gets to the electrics I think a diesel would also have stopped working due to the engine having water in it. Also if electric and water don't mix I take it your not fitting any electrics to your boat, including an engine with any electrical components.
Quite the opposite I would have thought, a good cruising boat will usually get good resale, a racing boat usually doe'snt get as good a resale.

None of the boat's I have posted have been racing boat's.

A rotating mast in reality only has 6 failure point's. 3 rigging screw's and 3 shackles. If useing rope shroud's and forstay less chance of failure again.

A frame mast's have been around for 30 year's that I know of, with limited success.

Just my thought's and observation's.

Dave
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Old 01-06-2007, 08:43   #60
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Quote:
Originally Posted by 44'cruisingcat
What's more important than the angle of the bow, is the location of the centre of lift of the hull. Many cats have it too far aft, and at speed the bows are depressed, generating spray. If the centre of lift is far enough forward the boat will tend to lift it's bows at high speeds, and generate little or no spray. There's a video here that illustrates it :

GUNBOAT Click on "Video" .

This boat is sailing very fast, and generating very little spray, even though it has perfectly plumb bows. Bows with a fine entry also reduce spray, compared to bluff bows.
Good point about the center of gravity. You still want most of your useable water line working for you. However it looks like that gunboat is in VERY calm water. Look at 00:49:00 and you can still imagine getting wet. I like the Gunboat!
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