Coronado 15 rotating mast mod

[walt]

I put this mod in this forum since the implementation is significantly copied from the Macgregor rotating mast design (includes speaders used on stays) and a couple recent post here got me thinking this was a good idea. The threads below have pictures of the Mac system which I used. Both of of threads are rotating mast mods to a 26D

http://forums.macgregor.sailboatowners.com/showthread.php?t=142896
http://forums.macgregor.sailboatowners.com/showthread.php?t=138272&highlight=rotating+mast


All the pictures of this mod are here
http://s359.photobucket.com/albums/oo33/waltcolorado/Coronado 15 sailboat/C15 rotating mast mod/
- there is usually a caption with each picture if you look at them one at a time.

I havent tried it yet... hopefully this week.

 

[walt]

FYI, the rotation I ended up with is about 45 degrees and its currently limited by the rotating spreader assy.

This is about what Im hoping for with 45 degree rotation

 

[justsomeguy]

Nice work! Looking at those drawings, it may certainly put a clean leading edge out there. Let us know how it changes anything.
Will there be any difficulty setting such a nice entry into the wind WRT the mast rotation? Force multiplier needed?

 

[walt]

I think this is where the position of the rotation front to back at the bottom of the mast comes into play.

I dont know - will find out soon.

 

[finding41]

Walt; Tell Cartman there in Southpark you are a genius!
Another thing to build when the water is frozen here.
Thank you.

 

[walt]

I took this 15 foot sailboat out yesterday - a big thumbs up for the rotating mast.

I had moved the rotation axis for the base as far forward as I could based on info I got here - this was a good thing to do as this really aids the automatic rotation of the mast. I think for this small mast, even putting the rotation right at the leading edge would have worked best. When I would tack, the mast would pretty much always rotate to the correct side but sometimes in very light winds it wouldn’t - but I could grab the boom and nudge it over into place.

In this case, the rotation is limited by the spreader and I’m getting probably just a little over 45 degrees. I think this is just a little too low but maybe not bad. Some pictures of what the sail looks like under sailing conditions with the mast fully rotated. I’m still not getting the very clean LEE side leading edge I would like - but its not bad. The only change Ill probably make is to further trim the speader assy to get a little extra rotation.

I went out with my son and while he was sailing the boat, I would manually rotate the mast back to center and then fully rotated. I could feel a significant difference in the sail lift generated. I can feel something similar with my Hobie 14 (rotating mast but no jib) but wasnt sure what would happen with the jib since it somewhat negates the need for the rotating mast. I think for this particular boat (which gets up on a plane fairly easily), this was a very positive change and its still very simple to setup. I think Ill see the largest benifits when it gets windy and Im sailing on the main alone.

 

[Sumner]

Nice Walt and good pictures that show what is going on. You are going to have to bring the boat through Blanding on one of your trips and take me out on Recapture Lake (the one north of town that the highway crosses the dam). We get some good wind there,

Sum

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[walt]

FYI, the attached picture is of a Hobie 14 rotating mast base. The pivot is forward but interesting that the base also has tabs that limit the rotation. The Hobie 14 has no spreaders on the stays.

Sumner, that is a pretty little lake. It must be close to 7000 foot elevation? I know you were thinking about some sort of day sailing boat for there, what are you thinking now? That lake is probably gusty so something with a lot of wind range would be good.

 

[Sumner]

...Sumner, that is a pretty little lake. It must be close to 7000 foot elevation? I know you were thinking about some sort of day sailing boat for there, what are you thinking now? That lake is probably gusty so something with a lot of wind range would be good.

Right at 6,000 feet. I know a guy here that would take a Hobie out on the lake and liked it, but his wife didn't. I don't know if he still has it or not. I need something that we would stay pretty dry in to extend the season on both ends. Looking at your boat gives me some ideas and I'd like to see it again,

Sum

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[walt]

This modified C15 is dry and I’m finding fast but… like always, there are tradeoffs. These were designed for two people racing – one person on a trapeze so it’s got a flat planning hull and all the ballast is the pilots. I didn’t know much about the boat when I bought it and found that it was just too unstable for sailing by myself so long story made short – ended up with two 80 pound bags of concrete plus a 40 pound battery all centered just under the mast base. There are some 4 gauge wires going to the back where there is a plug for the 30 pound thrust electric trolling motor which I like since it ends up putting only 13 pounds on the transom and moves the boat at about 3.5 mph for an hour or so without stressing the battery much. It has some similarities to the Mac 26S which I really like. It has a very light center board – easy to work on, nice clean shape, fully retractable and along with a kick up rudder, its easy to beach.

The “high” ballast also has some similarity to the water ballast boat – but it’s even higher in my modified C15. Righting moment due to ballast comes from the boat rotating about some center of buoyancy and lifting some mass. The lifting has to work against gravity so the movement of the mass in the vertical direction is what is important.

In either my little boat or a 26S, initially the boat is tender for a few degrees but this is because the center of buoyancy of the boat has to move from the center out to the side as the boat heels. But this happens quickly and as soon as the center of buoyancy has moved out, there is now a lever arm that is lifting the boats ballast mass.

With the high ballast, that mass gets lifted directly up at low heel angles – so effectiveness of the ballast is near optimal as pretty much all the movement is directly in line with gravity. That is also where this little boat is fast – you want to keep it flat as that is where you get the maximum righting moment force per change in heel angle. That flat planning hull and the ballast placed near optimum for low heel angle and high aspect underwater foils that don’t have the burden of carrying ballast – fast.

The trade off is of course if you ever get the heel angle high, the ballast mass is now just moving to the side and NOT lifting against gravity. So on this little boat, once you get the heel up fairly high, it is real easy to just keep it going on over unlike the lower ballast which really starts to stiffen up for the same condition. That is why I keep that Hobie Bob float at the top as this boat is not self righting.

This diagram below hopefully shows the good and bad of the unusually high ballast.

 

[Sumner]

This modified C15 is dry and I’m finding fast but… like always, there are tradeoffs. These were designed for two people racing – one person on a trapeze so it’s got a flat planning hull and all the ballast is the pilots..

Thanks for the info. Think of it as possibly the center hull of a very small trimaran with some mods to make it sleep-able overnight with a sunbrella enclosure. I want to make something like that and if I can use an existing hull and rigging for the center hull it sure would speed up the build process. This wouldn't be a world class racer, just something we could take out on the 3-4 local lakes and have some fun with. I like the shallow draft, retractable CB and kickup rudder,

Sum

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[walt]

Im not sure if the C15 is the platform to start with (might be small for the overnight requirement) but if you need any measurements to start getting a baseline, send me a PM..

I like the shallow draft, retractable CB and kickup rudder

Sounds like a 26S might also fit the bill

 

[Sumner]

Im not sure if the C15 is the platform to start with (might be small for the overnight requirement) but if you need any measurements to start getting a baseline, send me a PM..

Sounds like a 26S might also fit the bill

The S is too big for these lake, but other than that. I also want something that I can be in the water with 30 minutes from leaving the house. I'll get with you when we finally get home,

Sum

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Our Endeavour 37

Our MacGregor 26-S Pages

Our Trips to Utah, Idaho, Canada, Florida

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[walt]

Finally done??

I took the C15 out again with the rotating mast a few days ago in some fairly high winds and decided I need a "rotation inducer" setup similar to what Capt Kermie did on his 26M.

My setup is similar to the Mac in that all the rotation is at the leading edge of the mast. My sheeting is mid boom with a traveler (which I like) and when the sail is loaded up, the boom puts a forward force on the mast - i.e., the front end of the boom is pushing towards the mast. I’m not sure if this is because of my sheeting system or is simply because of the sail lift vector but it results in the mast rotation having two stable angles - correct and completely rotated the wrong way. I was sailing in the high winds (white caps) with just the main and just too often, I would end up with the mast rotated the wrong way and pretty much stuck. If I went forward and rotated it, the big change in lift would about upset this small boat and the resulting bouncing would end up with the mast at the wrong angle again.

So.. I added lever arm at the front of the mast so that I can pull it in the correct direction from the side I’m sitting on. Normally this lever at the front of the mast could get caught on the jib sheet but its under the wood mast guide. It should be an easy set up - just clip on the rotation inducer (one clip)..

I havent tested it yet on the water..

 

[walt]

Just a note on the rotation inducer idea I got here (from Capt Kermie) - worked really well.

I got to sail the boat in a lot of wind (that always comes along with a thunder storm this time of year) and in the higher winds, sailed on just the main. With the rotating mast well behaved - very sweet - hitting about 7.3 knots on reaches. Only problem now is that in high winds the boat wont tack with just the main so had to drop in the electric motor sometimes to get the boat to come around.

Overall... worth while change for this particular boat.

I thought the single position at the stop looked pretty good overall - but these guys fine tune the rotation http://www.youtube.com/watch?v=5Q0ovCn1Yxs&feature=related

 

[MrBill_FLL]

nice setup Walt. sort of looks like a 420/470

does water come up thru the centerboard slot?

 

[walt]

The centerboard slot has a gasket - which seems to keep water out.

There are a couple small planning boats called Finn's that sail on this lake that look also interesting to me (but am fine with this nearly 40 year old C15..). Video from yesterday http://www.youtube.com/watch?v=STOU27jnWsg&feature=plcp

As I said earlier, I got passed by a laser in similar wind to the video about 2 weeks ago (before the rotating mast). I thought you have a laser?

 

[MrBill_FLL]

yes, I own a laser... just wish I had time to sail it more.