Converting Marconi to Gaff Rig

[FSMike]

Originally Posted by tamicatana

You do realise that a "squarehead" main is effectively the same thing as a gaff rig, without having throat and peak halyards

And without the ability to scandalize it in the event of a sudden squall.

[FSMike]

Originally Posted by bruce smith

I swapped this boat, marconi to gaff.better for CRUISING

For some folks perhaps.
I lived and sailed for years on a 26' gaffer. I was very happy to go to a marconi rigged boat.

[David_Old_Jersey]

As this thread has popped back out of the ether........

........if someone was converting something like a 27' ships lifeboat from marconi rig (underpowered because underkeeled - sails sideways!), would a gaff rig (for the same height mast or less) result in a lower Centre of Effort or simply allow more sail up? - on the main, especially aft to balance out a (new) bowsprit.........(lets pretend the sailing sideways issue was addressed by dutch style leeboards!).

Mostly an academic question (I hope!) - but me father has discovered that one of his old boats (wood!) is for sale and cheap (3 guesses why - wood!), and he wants to rope me in (he's nearly 80).....one helluva sea boat, great on passage but only under power - always wondered what she could sail like.........

[Pauls]

Hi David,

A gaff rig will give you a lower center of effort, allowing you to carry more sail with the same amount of righting moment. The mast will be shorter than marconi. And as you mention, you will have more sail area aft so a bowsprit forward will balance it out. Gaff lets you spread a lot of sail down low where it is easier for the hull to carry it.

The hull you've got will perform best off the wind (underkeeled) and off the wind gaff is significantly more powerful than marconi.

If you do this I'd suggest you look at aluminum pipe for the mast. It will be significantly lighter than solid wood and is economical.

Regards, Paul

[David_Old_Jersey]

Cheers Paul - boat not bought and hopefully won't be!, but that outside my control.....but if it is then would be nice to do something useful with her at some point!

She already has an aluminium mast on her (on a tabernacle), was thinking about using that. With the spreaders lopped off (as rig less tensioned?) and maybe a couple of feet off the mast (mast not tall). My take is that the key would be the barge / lee boards to make such a substantial mod worthwhile even bothering with. Whether worthwhile to acheive anything being a different matter. In any event that one for the dim and distant future - if ever!

[Pauls]

Hi David,

Cool.

One thing to keep in mind is that because gaff can't have spreaders you end up with a longer length of unsupported mast. That means you need a stiffer, ie stronger mast than is required for the marconi. Marconi uses spreaders to divide up the mast into shorter sections that require less stiffness to resist buckling.

Cheers, Paul

[kefroeschner]

Just want to jump in here so I don't lose this thread. We are planning to go gaff-rig on our Morgan 45. Rather a high tech approach -- carbon fiber gaff for example, and highly peaked gaff, so it's almost a gunter-rig. My calculations indicate we will gain in stability, due to lower weight aloft (replacing 10' of heavy Al mast, 60lb, with the gaff at no more than 30 lb) and should keep the CE -CLP balance about the same. The AR of the main is just as high as with a bermudian and it can be a lot cleaner aerodynamically. The large diameter of the mast in the original rig renders the upper portions of the main essentially useless. With the slimmer gaff and a sleeve over it the upper end of the main is cleaner.

Also we can lower the gaff to get under 50' bridges, have less weight and windage aloft in storms, etc.

I'll post some drawings next time.

[Pauls]

I like your idea. I think that gaff rig, with the application of modern materials, has a lot to offer. Looking forward to seeing your drawings.

Regards, Paul

[kefroeschner]

These are a bit rough -- hand drawn over copies of Charley's original which I downloaded at poor resolution from the web. But at least the scale is right. We are keeping the lower shrouds and original mast section. The gaff pivot is not the old style 'jaws' but rather a 'gooseneck' fitting, just like a boom, which rides in the sail track up to a heavily reinforced section at the top where it bears. I calculate the maximum load at this point to be about 3,000 lb, which should be tolerable. The short gaff on the mizzen is really just a large headboard with a single halyard at the optimal point -- a rig recommended by L Francis Herreschoff and used in 'Rozinante.'
In addition to the jib shown, she will carry a boomed self-tacking staysail on a parallel headstay. The two together, with the stays'l guyed to weather should make a great tradewind rig, 575 sq.ft.

[Pauls]

That is a pretty boat. Truly handsome.

The original mast section should be OK with your approach of using the sail track for the gaff. I notice your plan shows no spreaders. Why not? The staying angle on your cap shrouds is very low without a spreader.

The high peaked gaff will do a good job of minimizing gaff sag to leeward.

It's good you're reinforcing the mast section where the throat will bear. I'd suggest doing the same at the points where the throat will bear when reefed down.

Your sketch doesn't show any runners. Are you going to fit them?

Regards,

Paul

[kefroeschner]

Paul:

Thanks for the compliment -- Mr Morgan deserves the credit.

The staying angle to the cap shrouds is 1:6.6, well enough below the recommended minimum of 1:7. It's better than it looks in the drawing because the shrouds also lead aft by 30 degrees, i.e. as seen from above the shrouds and headstays are at equal 120 degree intervals. So, no spreaders -- a continual source of chafe, windage and other troubles -- just one more thing that might fail

Yes, we might reinforce the track at the reefed position as well.

I do not think runners will be necessary due to the 30 degree aft drift of the shrouds mentioned above. They are 3/8" 1x19 with 5/8" t'buckles run directly through the deck to a massive steel 'jockstrap' in the boat's bowels. Runners could always be retro-fitted if it seems necessary, but I am striving for simplicity and strength as opposed to clever complexities.

Thanks again for the response.

kef

[Pauls]

Hi Kef,

Thanks for the details.

A point on design logic - the leading aft of the shrouds does not improve their staying angle on transverse loads. It does improve their ability to handle fore/aft loads. You can divide the loads on the shrouds into two components: transverse loads and fore/aft loads. These can be calculated seperately and then added together to get the complete load.

I went thru this design process on the rig for the boat I'm building, a 42' LOD double ender gaff rigged. You will definitely need to add the fore/aft load to the transverse to size the shrouds. Because the fore/aft staying angle of the shrouds is small, the tension on them to resist the forestay tension is significant. You can do this with a simple vector analysis which Francis Kinney describes in his book "Skeenes Elements of Yacht Design".

I think that you will find that while the swept aft shrouds will keep the mast up OK they will not keep the forestay as taut as you might want. Runners are good for that, and also for keeping the shrould loads down when you're running with a good wind behind you.

It's an interesting thing working out a modern gaff rig. They have great potential.

Regards, Paul

[britskip]

Hi, all the bristol pilot cutters i have sailed on already were gaff rigged, much the same as the brixham sailing trawler i once skippered, gaff rigged ketch??