How to measure mast height ?

[dart]

Any ideas for measuring mast height WITHOUT climbing the mast or using a sextant?

Ta Chris.

 

[StugeronSteve]

For what purpose?

 

[Evadne]

Tie the end of a tape measure to your main halyard and haul it to the top? Or a long bit of string, and measure the string afterwards?

 

[Superstrath]

easier - bring the end of the halyard to the deck, put a bit of tape round the halyard where it exits the mast. Hoist the sail, then measure the amount of rope you have pulled through.
OR-Use a stick, like a brush handle or such, then put your eye to the ground (or a point level with the base of the mast)and move the stick forwards and backwards until the top is in line with the top of the mast. Measure the stick, the distance from eye to stick, stick to mast, multply the stick length by the distance of the eye from the mast divided by the distance of the stick to your eye.
Think I saw that very old copy of "Scouting For Boys."

 

[eyupdougdown]

Hire a crane for the day, destep your mast but not before releasing the shrouds and stays. If you do not do this, well, you work that one out. Lay your mast on the ground and measure it. Use crane to position boat on its side at plain end of mast, attach mast then let go. Job done.

 

[fireball]

really ... it would be much easier to throw a stone (or other object) up from the bottom of the mast to the top, measure its speed and time it takes to reach the ground again - divide speed by time then divide by 2 (its come back down hasn't it) ... voila - the length of your mast ...

NB - don't forget to catch the stone or put a soft landing for it to fall on otherwise it might chip your gelcoat/varnish

 

[StugeronSteve]

Provided that the stone doesn't reach terminal velocity before hitting the deck you should be able to calculate the height from which it fell by the size of the gelcoat crater.

 

[Colvic Watson]

I know because we've tried this - the stone method won't work because the stone is still accelerating as it falls below the height of the mast and so there is no way to get an accurate time measurement. In order for that method to work you would have to throw the stone sufficiently above the height of the mast so that it is traveling at a constant speed for the entire length of the mast. We tried throwing, catapult and even considered attaching it to a mini-flare to get the height. In the end we resorted to using a tape measure attached to the main halyard. But then that led to a whole other set of problems with getting the chewing gum sticky enough to hold the halyard and tape measure together.

 

[StugeronSteve]

Re: Starling shites yer answer, innit.....

Wait until autumn and you've got em s(h)itting at the mast head, start the clock the millisecond that a little purple parcel leaves one of the blighters bums and stop the clock as you see, not hear (diff in speed of sound and light etc), it splat onto your deck. From then on it's simple maths, just calculate the suface area and mass of the turd, compensate for air density and any up/downdraughts, take away the number you first thought of and the job's a good un.

 

[fireball]

Re: Starling shites yer answer, innit.....

But thats no good now is it?!
Can I suggest a small alteration to your method - wait for a bird to land on top of your mast, shoot it with an airrifle and time its descent to your deck ... obviously you'll need to divide the time taken by the cuberoot of the fallratio of the bird (this is calculated by taking the weight of the bird + 5% - surface area of the bird * wingspan) .. this information can readily be taken from www.fallingbirdcalcs.com

 

[Colvic Watson]

Re: Starling shites yer answer, innit.....

Damn, didn't think of that. But then you mentioning autumn makes me think of leaves - wouldn't they be better as their slower rate of fall gives you more chance to get the timing right. You could have one person at the top of the mast dropping the leaves and another timing them. Just take an average.

 

[StugeronSteve]

Re: Starling shites yer answer, innit.....

You "Type As", you want everything now!

 

[Colvic Watson]

Re: Starling shites yer answer, innit.....

[ QUOTE ]
this information can readily be taken from www.fallingbirdcalcs.com


[/ QUOTE ] You got that URL wrong - it's .co.uk at the end not .com

 

[Strathglass]

Take a digital photo of the hull and mast from the side of the boat.
Print out a A4 sized photo then scale it from the length of an item on the boat (eg boom or overall length). If you are not too near you will find it reasonably accurate.

Iain

 

[StugeronSteve]

Re: Starling shites yer answer, innit.....

Only problem with that is getting the tree up there first.

 

[Roberto]

measure the length of the shadow of the mast and the one of a stick similarly held upright on land

what's the use of a sunny day ? /forums/images/graemlins/laugh.gif

 

[StugeronSteve]

Especially if you use one of those fish eye lenses, then you won't need to swim along way from the boat to take the piccie.

 

[Colvic Watson]

Re: Starling shites yer answer, innit.....

Don't be daft, you could grow one. Something like a sycamore wouldn't take long

 

[StugeronSteve]

Re: Starling shites yer answer, innit.....

Yer big soft plugger! You will need to know how tall the tree is, in order to subtract this factor form the overall result, and the b****y sycamore's gonna change its height innit?

 

[Thistle]

Measure the mainsail luff then add a bit for the distance between the foot of the sail and the mast foot.