MacGregorSailors.com

This would be a very interesting mod for a Mac: Fixed canted twin keels.

http://www.brayyachtdesign.bc.ca/article_twinkeels.html

In summary, this article describes boats with what are called twin bilge keels, which come off the hull like a shark's lower fins. When the boat heels, the leeward keel goes vertical in the water while the windward keel goes horizontal.

According to the article, this results in numerous efficiencies.

On a Mac:

--They could be setup such that the keels go over the trailer tires out to the 8' limit. Goat posts on the trailer would have to be moved forward of the keels.

--They could be permanently ballasted if you don't mind the increase in tow weight of about 500lbs. This would make the Mac far less tender. The windward keel ballast would become more effective due to leverage as it comes up in the water, meaning that you could have less ballast weight overall. My initial calculations show that two 250 lb. bulbs at the bottom of two 2 ft. keels would be equally effective as the water ballast.This presumes a 60 angle on the windward keel with 5 feet from the bulb to the center of buoyancy, which is essentially the distance from the bulb to the centerline.

--Planing would not be possible. The keels would make a planing hull unstable. The only reasonable solution here would be to hinge them so they could be raised vertically to get them out of the water, or to do this on a Mac with a displacement hull such as a 26D (which would be the right hull to mod for this IMHO).

--They ground completely flat. and boats don't have an issue with this, but most sailboats do.

Anyway, thought it was a very simple solution and I'm surprised I don't see a lot more of this. IOR rules forbid them apparently.

Well, when the tide goes out in Wales, it's certainly an advantage!

Yeah, we saw the same thing in Normandy--An entire mud-flat marina. Some boats were twin keeled but many just had lumber propping them up!

Plenty of bilge keelers here on the east coast of the UK, this is very often an easy and cheaper way for a drying out mooring. I looked at twin keelers before we bought Rockhopper. You do loose the shallow draught (and all those nice areas that others cannot visit) and I found them more difficult to trailer/launch. Definitely something to consider if you'd keep her permanently in the water, though, IMHO. There are boats with retractable twin daggerboards, that'd be something to consider ....

I like this concept. http://www.fanclass-sailing.com/EN/ It does draw a lot of water however.

robbarnes1965 wrote:I like this concept. http://www.fanclass-sailing.com/EN/ It does draw a lot of water however.

I remember that from Yachting Monthly in 2009. Very interesting. Just what happened to them ? Bad timing at the height of the world economic crisis ?

Hey Rob!

Hmmmm. The boats shown in Kevin's picture would provide a good solid platform for root canal therapy. Clearly, the precise scheduling of appointments would be essential.

- Brian (As if you needed any help dreaming your dream).

Watched the video of that canting ring thingy...pretty innovative if you ask me! Kinda freaky to see the mast tilt like that, but pretty good idea...

I'd like to also point out the beautiful blue hull color and the obvious high speed it obtains...

The twin keels seems like a decent idea - I wonder whether the performance is actually enhanced or whether they are just a convenience - double the drag, but better heel resistance maybe? Either way, I think trying to do it would be counter-productive toward what the Mac powersailor mission is...if you're going to have fixed keel weight of any kind, don't bother with things like planing hulls and such...they just don't mix well. The Mac is truly a cool blend of practicality and forethought that is aimed at a specific niche of boaters. Now, as mentioned, if you wanted to modify one of the displacement hull boats, that's not much different than mod'g a "real" sailboat with twin keels... You could pretty simply make them retractable in some way, whether as swing-keels (no bulb) or as daggers (with bulb), and being shorter in length they could probably be incorporated into the interior space pretty easily. Would be a neat idea to see implemented.

You know, with that in mind...what would be the difference between that and just adding a "counterweight" that moves from side-to-side on the boat, instead of having something sticking down in the water, just moving from one side of the boat to the other to counter the heeling effect? You could probably use small daggers or even just increased chines to resist leeway...and just have a shifting weight to counter the heel. You might be able to make it smaller in weight than a ballast bulb, if you could move it out from the center - kinda like an outrigger, but not something that goes in the water...

vizwhiz wrote:what would be the difference between that and just adding a "counterweight" that moves from side-to-side on the boat, instead of having something sticking down in the water, just moving from one side of the boat to the other to counter the heeling effect? You could probably use small daggers or even just increased chines to resist leeway...and just have a shifting weight to counter the heel. You might be able to make it smaller in weight than a ballast bulb, if you could move it out from the center - kinda like an outrigger, but not something that goes in the water...

The problem is inherency: How do you ensure that the counterweight _always_ moves when is counteraction is needed and never moves when it would destabilize the boat? Just a few seconds of having the counterweight to leeward when the boat heeled suddenly could capsize it before the crew could move it.

I'd been thinking about some sort of mechanism like the "ring" mechanism that would cant the keel automatically when the mast tips. The ring mechanism solves it, but it looks frankly very complicated. My plans were in taking just the stays around the hull down to the keel bulb using fairleads and not worrying about the drag they cause. Would be considerably simpler. But I'm never going to do it.

I like the twin bilge keels idea a lot. If I ever designed my own hull, that's how I'd do it.

FinallySailing wrote:

robbarnes1965 wrote:I like this concept. http://www.fanclass-sailing.com/EN/ It does draw a lot of water however.

I remember that from Yachting Monthly in 2009. Very interesting. Just what happened to them ? Bad timing at the height of the world economic crisis ?

Yeah, not much news coming from them. I saw 3 of the 2008's for sale on a site yesterday when I went back looking for the link. That is probably the whole fleet. I expect they gave up on it. I thought it was a very cool idea. But you do need a lot of money washing around to get an idea like that going - especially when the sailing community is still having trouble with accepting simpler concepts like roller furling.

Ha Brian! Yes, adding tide tables to dental scheduling - now that would be fun training the secretaries.

Vizwhiz , here is your answer to keeping the stabilizer internal. http://www.seakeeper.com/ The only small problem would that it costs more than a new Mac!

Mastreb, we are awaiting the retail version of your mod kit

I have thought about this a few times
1> first make the rudders canted with modified rudder brkt's with straight up/down vertical lift this would let u use them in shallower water maybe even add small wings to them not sure if that would be an anvantage though "wings" that is
2> I would go with extenally mounted canted keels mounted on an inverted "H" brkt that could be mounted on the deck @ the chain plates area of the deck & hull as their re-enforced in that area to start with the keels would be made from very thick plastic with a small bulb on the bottom they would be hollow inside to allow for water ballast thus solving the weight issue while powering or trailering the inverted "H" brkt could be mounted on a hinged brkt to allow for forward or rearward movment for best perfomance or on some kind of "T" track
3> The addition of another hinged "U" channel brkt mounted aft @ the transome would now with 4 sections of 3" thick wall Allum. tubing 8' long with a deck plate on each end could be mounted to these 9' sit on plastic kayak's now u can have a tri & removeable kayaks
Theirs just no end in sight for the mods that can be done to this boat & me being very handy & capable of making this set-up the cost would not be to bad

J

Highlander - maybe a diagram for your thoughts on this mod?

I too would like to see a drawing. What I'm envisioning from your description I would call leeboards.

some links
http://www.duckworksmagazine.com/07/how ... /index.htm

http://sailcanoe.com/sailcanoe.html

these are some samples from smaller boats I will post more later when I get home

J