Measuring Guide


IMPORTANT – This guide should be used in conjunction with the downloadable measurement form:

OK, you’ve got it all prepared – the weather is at worst acceptable (less than 15kts breeze, not raining or snowing too much!), but let’s assume a best scenario and that it’s a still, warm morning; you’ve got a long non-stretch tape measure (metal preferably) and a length of string long enough to reach the top of the mast; plus a stiff ‘carpenters’ style 5m tape measure; and you’ve got our measurement form on a clipboard with a writing implement to hand. Ideally your boat will be alongside a marina berth too.

First of all, grab the best moment and prepare to hoist the long tape. This is where the string will be useful: we’ve broken too many tape measures and lost too many halyards up the mast not to advise tying the string to the halyard as a retrieval line, should the worst happen!


For the main halyard, there’s just one measurement to do with a tape up the mast, P, either from the black band, or from “max hoist” straight down to the top of the boom at the goose neck. Bear in mind your halyard may not have been that high up before and your splice may wedge in the mast sheave – this is where that string may become useful, as tugging on a tape measure can break it!

While you have the tape taut, and right in the crook of the gooseneck, it is in a good position to use as a reference for pre-bend (Section 3) – ease the backstay right off and use the width of the mast as a guide, then tension the backstay as far as it will go (we mean this!) and estimate again. Finally, while the tape’s still up there, estimate H.

If your mainsail furls, attach the tape and string to the bottom attachment on the top swivel and hoist to the top – bearing in mind that it may not have gone that high for a while, and therefore hoisting slowly and carefully towards the end so as not to wedge it up there. Take P in this case to the tack attachment point on the furler. Then cross through X, Z and Section 3 on your form as they will not be relevant.

Now get the tape down, and if you’re measuring for a Genoa too, hoist it per the instructions below, while the weather holds!

Next attach a tape measure to the back of the mast: there are a variety of ways to achieve this (string, an assistant, etc), but the measured part will need to be toward the aft end of the boom, so make sure there’s somewhere to stand and read there. E may be taken to the for’d edge of the black band if you have one or to the end of the boom casting. If relevant, also take D now.

Before you take the tape off the back of the mast, check X and Z too, preferably with each option held in the approximate position it will be in whilst in use. Detach your tape measure and take Y and BAD whilst at the mast, and also take a moment to inspect any existing sail for luff rope, foot rope and slide details (see Section 2), and cast around the mast for any manufacturer marks to record too.

The final measurement is C, so take that now, and if the sail has spilled out grab the opportunity to inspect it for logo and sail number, and check this is what you were expecting.

Finally, tidy up – this is sufficient information to make a mainsail to!


There are two possibilities here:

  1. If you are measuring for a hank on sail attach the tape (and string) to the halyard shackle, and hoist it to the top – be aware that like your main halyard there is a chance the splice will catch in the sheave, and that retrieving it using the string is easier and cheaper if it does – then measure FL, I, and MH.
  2. If you are measuring for a furling sail, attach the tape (and string!) to the head attachment point on the bottom of the top swivel and hoist to the top of your furler foil. With these, there is a chance of ‘wedging’ your top swivel at the top of the foil (depending on age, installation, whether you have a diverter, etc), so as you approach ‘max hoist’ slow the rate of hoist and keep backing off to ensure this doesn’t happen. Measure LL. FL is a useful check measurement so re-hoist your tape/string on the halyard alone and take this – and I and MH while you’re there.

On your way back down, estimate the spreader heights for section 4b, which is easier if you are not attached to the foil! Alternatively, use your spinnaker halyard (and string) to do this.

Assuming you don’t need to measure your P distance for a mainsail (see previous section), tidy up your halyards again – this is the last time you need to send your tape measure aloft.

Next, identify your forestay lower pin, and attach a tape measure to it – there are a couple of measurements to take from it: FEF to the for’d position your genoa could sheet to; J to the base of the mast; then vertically to D if you’re sail furls (and define on the form your tack attachment type). Then detach the tape for the last few measurements.

Whilst you’re still on the foredeck, take a moment to fill in section 5 as much as possible – pay particular attention to the make/model of any furler, and which side UV you need! C is relevant for furlers and foil sails and can also be done whilst you’re there.

F is good to take now, as well as OCL1 and OCL2 – a certain amount of eyeballing is needed for these as they want to be taken as a perpendicular measurement, and not many centrelines are at the same height as the track! Whilst your eye is in, measure your cap shroud base off centreline for section 4b, and estimate the length of your spreaders.

Take out your stiff tape measure, and go round measuring all the measurements related to the waterline: G, K, H, L, Q. H in particular can be difficult to take whilst on board, which is where a marina berth will come in handy, and an assistant even more so. When you’ve taken these, take a moment to rinse and dry your tape – it may well have been dipped in the sea.

Finally, tidy everything up, and place the form somewhere safe to send back to us – you’ve measured your boat for her new headsail!

Remember that we need to receive these measurements in as unambiguous method as possible: the most preferable is via email, followed closely by a physical copy posted to the loft in Wareham

As soon as we receive them, your measurements will be queued for designing your sail: if you have any specific requirements, this is the time to let us know them!