Waterline

Last time i was out sailing, i was out on the trapeze and decided it was a good opportunity to play around with and see how the boat sits in the water by adjusting my weight forward and back. My question is, whats the best waterline for the mossie when sailing upwind?

At one stage i had my weight forward which lifted the sterns completely out of the water, the bows were further down into the water, but not completely under. I know i need to stop the sterns from dragging, but how far up do i need to get them, as when i get them right out of the water, the waterline doesnt extend right to the rear of the boat, reducing my waterline.

From my understanding the longer the waterline, the greater the potential hullspeed through the water.

So my question in more detail i guess is, from personal experience, I know wind speed and waves play a factor in weight placement, but what is the optimal compromise between waterline and stern drag, where do u try to and get your waterline to be on the hulls when sailing on windward legs in relatively flat water, flat enough to not have to worry about waves or pitchpoling, i.e. such as half way up the bows to the very bottom of the very back of the sterns. Do you try and make the waterline as long as possible, or make sure the stern never drags, which should be the greater focus? Does anyone place visual aids on their boat to try and line up with the water for optimal waterline (i.e. marks on bow and stern such as from a marker pen)

Thank you,
Michael.

Hey Michael,
Some one said that 1 in 10 waves should go over the nose.
Thats how I try & sail if it is flat Im right foward with the bow just out & dipping in every now & then.
I suppose You could test it with a gps.
You can usuly feel if it is slowing you down.
Im not the most experenced mozzie sailor but thats my opinion
Cheers

Michael,

correct about length of waterline and speed, baSic naval arch.
Theory is sterns just clear enough for no drag and the rest is practice to see what works,

What works in theory tho' does not always work in practice.

Have fun tho'

David
Salpicon de Resplandor, Mosquito 1744.

If it feels fast it probably is!

You can feel the boat slow if you dig the bow in hard. You can also feel the boat slow if it does a lot of hobby-horsing - which happens more if you stand back.

There is a rule of thumb I've heard that when a hull is more than 6 times longer than it is wide then the waterline length becomes less of a factor in limiting speed. That's why the Moths evolved down to 250mm wide before they moved on to foils. So for a Mozzie, yes that extra little bit of waterline length will help, but other effects are more important.
Try to keep the boat steady so the sail(s) can keep driving hard, and don't let the transom drag.

I've never seen markers on the bow of a Mosquito.

Michael,

One of the old salts around the club supposedly said that if you burried the Mozzie bow up to the deck then you didn't need to rely as much on the centreboards to stop sideways drift. Mind you, way back then the Mozzies sliced through the water rather than floating over the top. I suppose it was a double benefit, limit the drag by keeping the transons out of the water and assist the centreboards.

No need for markers. Just listen to the turbulence or lack of it from the transoms.

See what effect moving backwards and forwards has on weather helm. The effect may only be small but anything that can assit in preventing weather helm will make you go faster.

Regards,

Peter

Hull speed for a 16 foot long boat is just less than 5.5knots. So if you are going faster than this you are in the speed regime that you should be "planing", ie you are going faster than a wave of the same length as your hull. There is a transition regime called "semi-displacement" but it is a fairly small range.

Typical upwind speeds for mozzies in 15 knots of breeze are about 11-13 knots (GPS readings on my old boat, others may get different readings) so well within the planing speed regime. At these sorts of speeds transom drag isn't as significant as skin friction.

But this isn't the whole story, as mentioned above, burying the bow affects helm balance and leeway angles due to shape of the bow.

Typically on most boat, stay well forward in the light stuff, move back a little as it gets heavier.

Really basic rule of thumb is your transom should always be dry. If you're going fast this is easily achieved, if you're going slow and the water is re-attaching to the transom, then you either need speed up or get the transom out of the water.

Thanks for the advice guys, and keep it coming if anyone else has more. Ill keep experimenting on the water.