Mast setup, pls comment

I have a question pls.

On the aft mast setup it is easy to furl the big sails and use a small one in high wind conditions, how would one do this with a bermuda type rig ?

 

You have plenty of options, working down head sail sizes, reefing mainsails, inner stay sails, storm mains and head sails. All depends how you want to set it up... Some of the modern boom furling setups are great, Hoods one I have used extensively. Rolling head sails you are familiar with.

Fannie, with that aft mast setup I think you will have trouble with fore stay tension and furling systems working correctly. If you do go that route be sure you can get the tension. Also personally I don't see how the rig will balance correctly, It looks to me like the center of effort will be to far aft... but I am no designer, have you worked all that out?

With this fishing lark you might find that a sailing multi is not as maneuverable as you need, they need speed to turn well because they are light with relatively high windage. They lose speed like no other boat I have sailed. I sail onto and off my mooring all the time, I virtually never use the motor. The speed at which I can turn into the mooring and the distance in which she stops would astound most mono sailors... its like doing a parallel park with a hand brake turn

Once you lose speed hull windage tends to become the overriding force, with boards up at slow speed you can lose allot of control, with boards down things are better but even with a single engine running you can still be at the mercy of the wind for periods of time, in certain circumstances. Sailing you will not want to be making a series of direction changes in a short space, (downwind not such and issue), you lose speed quickly and maneuverability goes with it. If you have twin engines and are motoring then you are better off but still not a craft you can spin around chasing fish easily. I have no idea what you need to do what you want in terms of handling for fishing I just thought I mention that slow speed handling issues, more so in a breeze, are a legacy of a light fast craft with high windage....momentum for low speed handling is lacking.

Not wanting to pee on the parade, just something to consider, maybe experience a bit before you finalise the design.... but then maybe you are on top of all that all ready

 

Hi Meanzie,

I have just been outside looking at the little tri I built to test the aft mast setup with, and I made a discovery I never thought of before. It is almost exactly half the size of everything I worked out for Cattrine ! The mast is 6m... I want two that is 12M (maybe 13m), the tri hull is 5m5, I'm going to 10m, The tri sail foot is 5m, I'm going to 7m - 8m.

The only single problem I have with the little tri is keeping the forestay stiff enough, the mast only a few allu pipe extrusions sleeved and OD is only 55mm. I can bend it some by pushing down on it while holding the other end in my hand, so it's not that rigit at all.

The beams I made for the tri are 4m long. Their ends supported I can stand with my fat butt (95kg) on them and they give very little. This may be the way to go with an aft mast - a very rigit pole that gives just about nothing.

There is something about the aft mast sail I like very much. The sail makes lift, this is nice since the amas doesn't get pushed under like with the boom setup. The amas hardly gets pushed under, maybe 50mm or so on a reach, while my friend's tri with the bremuda I sail the leeward hull right under the water like in there... it's gone, water and spray everywhere at 22km/hr (11kts).

I haven't been in some hard wind with my little tri yet since the wind dies down when I get to the water every time Really ! I did however get the impression that one can go on the plane when running if the wind is up to it.

The little tri points right on a close haul, but since I haven't a daggerboard (or keel) the side drift is significant and I don't reach target. My top speed so far isn't too great, only 12km/hr (6kts)... sucks eh I have what you can call no wind syndrome.

The furling of a bigger sail - Since I make my own furling roller I can easily determine the force-to-furl ratio by increasing the rope drum diameter. The larger the diameter the easier it would furl. You have to let the clew rope out to release the tention in any case, but this isn't a problem either, the sail flies up and out of the way.

Haven't told about Cattrine ! yet... female of course Not enough problems so complicating things a bit

Fish are funny creatures. When the take the lure they seldom swim in the right direction. It's mostly in the direction of most resistance, away from you. For instance if you trawl you hook it when behind you, they either go sideways or backwards so things happen really quickly. I get land sick just thinking about it

Each hull gets an outboard. Manuevering is not that big a problem though. As for a hand brake turn, I'm not there yet.

 

If you are willing to rerig your fishing gear when you change tacks, could you do a proa instead?
One unstayed mast with fullbattened sail (or 2 if you like).
Only one motor needed.
When a fish is on, loose the sheet and the boat will lie ahull. To back down, take up the other sheet (=shunting).
If you lose the fish, shunt again and put out your lines again, or rerig them to run out the other way....
Maybe see what Mr. Denney thinks...

 

Hi BWD,

He he... some brilliant drawing there Could put you up there with picasso.

I have had a look at proas. I don't like the idea and I don't think it's the thing for me. Looks like a tri that lost a hull

 

Is there a specific ratio between mast height and and boom lenth ? Or is it a discression thing.

 

..more extensive comment in a few days...meantime since you are looking at all kinds of ideas, have a look at a few of these:

Valkyrie catamaran...bi-pod 36" cat
http://boatdesign.net/forums/showpost.php?p=106915&postcount=31
(regrettably link no longer works)
http://boatdesign.net/forums/showpost.php?p=110509&postcount=38

Under "Main-less Rig"
A-frame rig sailing well
http://boatdesign.net/forums/showpost.php?p=184703&postcount=11
http://boatdesign.net/forums/showpost.php?p=184941&postcount=21
http://boatdesign.net/forums/showpost.php?p=185146&postcount=28
http://boatdesign.net/forums/showpost.php?p=194774&postcount=73

..another A-frame
http://boatdesign.net/forums/showpost.php?p=185402&postcount=33

 

Thanks Brian, looking foreward to it.

I have a question regarding sails.

The sail is cut when made so it creates s curvature theat makes a vacuum to the leeward side of the sail, right, so the boat's sail get sucked into this vacuum which propel it foreward, similar to an aeroplane wing.

Now an aeroplane has a lot of speed going for it, sails on the other hand rely on the brute force of the relative slow wind, hence the larger the sail the more propel power a boat has.

Now if one looks at the curvature of a sail then it seems that only the foreward third is curved, the rest seems to flatten off, so this is where the most efficient force is created.

Also, one sail curving around another ie, a bermuda rig with a jib, it seems the jib enhances the bermuda's performance by channeling and so accellerating the wind moving past behind it, besides that the jib's leading edge also creates a foreward force.

Now if this is true, why haven't sails a few vertical slits in them with spacers connected to vertical battens to control the 'vent' opening ?

Logic tells me this way one could have two, three... four... five leading edges enhancing one another while making foreward propelling forces instead of just trying to rely on one big unenhanced force which is more heeling the boat over instead of propelling it foreward.

Am I missing something here ?

 

Presently working on a new posting on this subject that will appear over in "Sail Aerodynamics"....but it is a week away at least:

Has to do with this paper that Tom Speer has referenced so many times. Does anyone have a PDF file of this paper??
http://boatdesign.net/forums/showpost.php?p=9987&postcount=15

http://boatdesign.net/forums/showpost.php?p=9987&postcount=24

http://boatdesign.net/forums/showpost.php?p=9987&postcount=60

 

Here's something on it too. Tom Speer seems to be a very clever chap, don't understand a word he says At least it seems his head is screwed on properly. If only one can get him to tell it in plain English

http://www.boatdesign.net/forums/showthread.php?t=1253&highlight=Kipling's Just-So Stories.

 

I had a look at Tom' web site -
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
No, I'm not going to get involved with this
...............

Pls consider the previous two posts by me cancelled

Think MASTS... MASTS

 

I can only speak drom the little experience I have with it and trying a little bit of common sense.

If the centre of sail is between the rudder and daggerboard the rudder has to help the daggerboard, so more side force would be experienced on the rudders, should not be a big problem if they are designed for it. We South Africans overdo everything

 

You need the center of effort to be just behind the boards from my understanding. I think that a quick way to estimate it is to draw a line from the mid points of the sides of the sail to the opposing corner. (?)

Have you got a backstay planned? Maybe a back stay with spreader, because the angle will be tight (-15 degrees) will provide the stiffness required. Forestay sag will show up alot more in higher winds, if you get sag in low or no wind it will be pronounced in 25knots of it. My rig is quite tight at rest but the flex in the boat makes it sag in a breeze.

Cheers
MBz

 

Hey Fanie,

I also love fishing. Great game fish out here in these waters along with decent size mahi mahi and all types of tuna. I was just in a fishing tournament a few weeks ago and was asked to be a firstmate/photographer onboard a 51' enclosed flybridge Riviera (has a tower on it as well). Was a beautiful yacht! On the second day we decided to go to to an island that usually has good game fish but it was a 2hours and 40minutes run at 20knots. That day we had burned almost 1000L of fuel on that day! The gauges showed we were burning 90+L/hr when we made those two long runs. When we were trolling we were burning 17L/hr. I would love to get my hands on enough money to be able to own and be able to support the fuel and maintenance costs..lol

But from my experiences on fishing cats haven't been so great. They are hard to maneuver when you have a blue, sail, or black on the line. I used to run a small 24' cat with small twin 50hp outboards. A few times we had a blue on the line I couldn't keep up with it due to there speed (as i take it you know). Also you might want to look more into having a boom and having you sail furl into the mast and having your boom pull up to the mast. That way you wont have any problems with it being in the way (haven't read all the posts but im working on it so excuse me if i am saying the same as someother people said).

I also think if you have your mast(s) in the back of your hulls they will get in the way for your angler. What happens when you have a fish on the line and your fish goes from the starboard side across to the port side and keeps going? your line will possibly be rubbing on the mast.

Are you planning on building her or having someone else?

This is just what i think

Jordan