22/10/2023 at 11:06 pm #26194Merlin3189Participant
I’m currently helping a few new members from our late summer L2 course. They learnt in Bahia and are sailing Bahia or Quest.
I feel it’s time to try a proper boat, as we have a couple of GP’s needing sailors at the moment, and we’d like to increase the number of GPs racing.
My question: the sailors are centre mainsheet: the boats are stern sheet. Do I convert the sailors or do I convert the boats?
My boat has previously been fitted with centre main to accommodate such beginners in the past, but I changed back afterwards, because I usually sail single-handed and like to sit in front of the centre main location. The newbies will sail only double-handed for now.
We already have enough spare parts to do a conversion on two boats.
People’s thoughts would be welcome.
22/10/2023 at 11:56 pm #26195
I think the short answer has to be “Your choice; either would be reasonable”.
However some additional points may be helpful.
First, the general consensus seems to be that the almost ubiquitous split-tail mainsheet led up to the boom from the quarters and then along the boom and down to the centre – which is very far from true centre sheeting – is probably the optimum system for racing, while traditional transom sheeting is probably (undoubtedly in my personal opinion) be fay the better option for cruising. Several reasons for those choices:
For racing, it is helpful to be facing forward when tacking or gybing, because these will often be in very close proximity to other boats, and gybes will often (and tacks sometimes) be close to fixed geographical locations (i,e, the windward mark and the gybe mark). Added to that, with a modern rig with a kicker powerful enough to control the shape of the sail without needing the mainsheet to help flatten it in stronger winds, the split-tail sheet effectively always sheets the boom to the windward quarter; this gives by far the most effective sheeting line, and thus for a given wind load and desired boom position it minimises the load on the sheet needed to hold the boom there. That is why there is no need for a multiple purchase with this arrangement.
For cruising, all except the last of these considerations are irrelevant, and conflicting considerations become much more important. Close proximity to other boats will rarely if ever arise, and you normally have almost unlimited choice in the location of where you tack or (more importantly) gybe. So there is no requirement to face forwards, but it is very helpful to be able to face aft during a gybe, in order to choose your wave (or your “smooth”), and gybe at the optimum point for the following seas. Add to that the much greater space in the cockpit, which becomes important if you have more than two persons aboard, and the balance swings heavily in favour of transom sheeting for cruising.
A third consideration is that there is a benefit in trainees having had experience of both sheeting systems; so if they have initially learned on centre sheeting it could well now be time to give them valuable experience on transom sheeting.
Hope this helps,
- This reply was modified 1 month, 1 week ago by Oliver Shaw. Reason: typo
23/10/2023 at 5:49 pm #26197sw13644Participant
Oliver makes very good points and I agree with them all, and also…
If you are hoping to help some inexperienced helms transition from sailing a Bahia to a GP14, I recommend that you make as many things as similar as possible between the two vessels, to maximise their immediate comfort and recognition of things learned when they step into the GP14.
Learning to sail has a high cognitive load for beginners, and some people are already overloaded with incoming senses – it is a highly kinaesthetic environment – before then learning to sail a boat that will feel very different – tiny, nimble, tippy compared to the Bahia.
So my recommendation is to fit the centre main, using a split tail mainsheet if you can (minimises mainsheet rope length), and maximise their familiarity with techniques already learned.
23/10/2023 at 10:09 pm #26198Merlin3189Participant
Thanks Oliver and Steve, for interesting and useful comments.
I’ll have to look into the details of split tail main. Mine has a rope horse, which I’d have thought similar. Not needing so much MA on the mainsheet sounds useful.
I’m tending towards the centre option, for Steve’s reason. They might be swapping between boats and lot at the moment, so I don’t want to cause confusion. Plenty of time to try stern sheet later. But they’re all pretty keen and smart enough, so I’ll talk to them about it.
24/10/2023 at 8:49 pm #26199
A rope horse may or may not be very similar to a split tail mainsheet, depending entirely on how it is configured.
There are two key characteristics of the modern split mainsheet, one of which is that it is ultimately led to the centre of the boat, which many see as a benefit when racing, and which you see as a benefit for your purposes (because your students are already familiar with that arrangement). The rope horse can be ultimately led forward in exactly the same way, but it is more usually led to the helmsman direct from the transom; and that decision is a matter of your own choice, for your purposes.
However the other key characteristic of a split tail mainsheet, which is a benefit when sailing on a course, particularly to windward, (but can be a minor disadvantage during a gybe), is that – provided it is set up so that the joint is close to the boom when close-hauled – it always automatically transfers the load to the windward quarter. Effectively the leeward tail will be carrying little or no load, and may even be slack; but it takes up the load as soon as the boat comes onto the opposite tack. Whichever tack the boat is on, the boom is always sheeted to the windward quarter; and that makes for a system which is particularly effective for controlling the lateral position of the boom. The converse of this is that it exerts much less downward pull on the boom, and so does little to help flatten the sail; but with modern powerful kickers there is no longer a requirement for the mainsheet to control sail shape, as that is adequately controlled by the kicker.
As a result, the split tail mainsheet does not (on a GP14, and other boats of similar size) require any “purchase” (mechanical advantage, gained by block and tackle) in the mainsheet.
How closely, if at all, your rope horse comes to this configuration depends entirely on how it is configured. At one end of the scale, if there is little slack in the horse when it is not under load, and the mainsheet block is free to run the full length of the rope horse, always remaining close to the deck, and with no control lines, it is a radically different system. In that arrangement, the boom will always be sheeted to a point somewhere between the centre and the leeward quarter, not the windward quarter; the sheet will exert a significant downward pull on the boom when hard on the wind (which may help flatten the sail if you have a kicker of only small purchase, but this will be irrelevant if you have a modern powerful kicker); and it will not be particularly effective at controlling the boom laterally, so you will need a purchase of at least 2:1. A few helmsmen prefer 3:2, which offers greater mechanical advantage but also (of course) greater velocity ratio, so there is that much more rope to pull in or pay out when needed. However most helmsmen find 2:1 sufficient, and prefer that ratio because there is less rope to pull in or pay out.
However if your mainsheet is secured to the centre of your rope horse, instead of being free to run along the horse, then it starts to become closer to the split tail arrangement. It is now in effect one version of the split tail arrangement, but only if the horse is long enough for the junction of the two ropes to rise well above the deck, indeed fairly close to the boom when hard on the wind. In that arrangement the windward side of the horse will (perhaps approximately) line up with the actual sheet, while the lee side of the horse will be slack; and in that mode, but only in that mode, it will perform just like the split tail mainsheet – but the latter is simpler and neater.
In between those two very different modes you might conjecturally have the sheet permanently secured to the middle of the horse, but the length of the horse permitting that joint to rise only modestly above the transom. In that scenario it would be a half-way house, and the characteristics would be somewhere between those of the two different modes.
Hope this helps,
10/11/2023 at 10:22 pm #26256Ian RParticipant
I too am interested in the choice between transom or twin tail mainsheets.
I am contemplating buying an early fibreglass GP (sail number in the 9000’s) which has a horse integral with the aft deck.
Would it be possible to fit a centre mainsheet block on the aft end of the centreboard case and then convert the main sheet to a twin tail system? Would the top of the fibreglass centreboard casing be strong enough to take the load and would there be enough thickness of material to take long enough screws?
Any comments or observations would be greatly appreciated.
10/11/2023 at 11:01 pm #26257
The short answer to your first question is that transom sheeting tends to be the preferred system for cruising, and the twin tail system led ultimately to the centre tends to be preferred for racing. See the second post in this string for the reasons. There are some owners who regularly do both who have arranged their boats to be readily interchangeable between the two systems for that reason.
The second question is an engineering question, and if you consider the existing structure in standard format I very much suspect that the answer is no, but I am sure that it should be reasonably possible to beef it up sufficiently to take the load. There are two separate issues here; the first is making the top of the case strong enough to take the load – including transmitting it to the sides of the case, and that may perhaps be most easily achieved by spreading the load, while the second is giving sufficient grip for the screws or bolts. The latter is actually a separate question. Bear in mind that your centreboard case was never designed to take a sheet load, because that was not permitted in the Class Rules at the time your boat was built.
Cue now for someone with intimate knowledge of this part of the construction of Mk I and II GRP boats to step in, please. … …
–o0o- -o0o- -o0o- –o0o- -o0o- -o0o-
Failing that, I would assume that it is not currently strong enough, so you need to beef it up. It is a straightforward laminating task to add some more fibreglass, and personally I would use woven glass tape in preference to chopped strand mat, for both strength and appearance. Use epoxy resin, of a type specified for laminating, not polyester; the headline brand is WEST System, but there are others, and supplies are readily obtainable from most yacht and boat chandlers. Please be aware that the stuff sold by car accessory shops tends to be poyester resin, not epoxy, and this is NOT SUITABLE!
Although epoxy resin is significantly more expensive than polyester it is vastly stronger, so you don’t need as much of it, which goes some way to offsetting the higher cost. But much more importantly, polyester resin does not adhere well to most substrates, including not adhering well to cured substrates of the self-same resin, which is one reason why in manufacture it is laid up wet on wet; it adheres well to itself provided the substrate is not yet cured when it is applied. By contrast, epoxy resin is an excellent adhesive that adheres well to most materials, including to cured polyester resin. Your boat was built with polyester resin, but it is epoxy which you need for any repairs or modifications to it.
Build up the thickness of the top surface and also continue the overlay for a short distance vertically down each side of the case; before applying new resin and laying up the laminate prepare the surface first by abrading, and then thoroughly cleaning off the sanding dust (by first dusting it off mechanically and then use a cloth dampened in a suitable solvent/cleaner). That should give adequate structural strength, and for the sake of cosmetic appearance you can then if you wish overcoat it with either thickened epoxy or a suitable filler, and then sand it smooth, and finally paint it. Alternatively you could cap it by bonding on a hardwood capping piece.
Of course, do your “due diligence” before laminating – in this case by abrading the substrate. I suggest a power sander, preferably an orbital one, followed by thorough cleaning to remove all traces of sanding dust,
The problem of obtaining sufficient grip for screws is more complex. You will still have only limited thickness of GRP, and ordinary screws do not cut into this material at all easily, so you end up drilling out almost the full diameter of the screw – which means you have even less grip. Options include the following:
- Screw into pre-drilled holes almost the full diameter which are first coated with epoxy which has not yet cured; screw lightly without fully tensioning the screws, wait for the epoxy to cure, then heat the end of the screw with a soldering iron to soften the epoxy and screw it in tight.
- Create drilled and tapped holes, and use bolts. See the Gougeon Bros technical manual (available as a free download on their site) for details of how to do this.
- Bond in fixed upstanding bolts; again see the above technical manual.
- Bond in fixed upstanding bolts passing through a stainless steel plate bonded into the new laminate, with the laminate continuing over this plate.
- Anything else that the above technical manual may suggest.
As you may gather, the job should be doable, but it seems (to me) likely to entail a modest amount of fibreglass engineering.
While you are doing it you may wish to fit a central pillar to mount the swivelling sheet block (plus jammer if you decide to fit one).
Hope this is of some help.
- This reply was modified 2 weeks, 5 days ago by Oliver Shaw.
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