Daggerboard location on 9' fiberglass sailing Dinghy

Hi there!

This is my first post and I am new to boat building. I am a young person who wants to get into boating and sailing. I have a 9' Davidson style Fiberglass dingy (in pretty rough shape when i began!) that I am currently restoring. The boat has a hole in the hull for a daggerboard but I think its the wrong position. I want to put a lug sail in the front of the boat and will have to move the daggerboard location forward. I am not sure where the location of the daggerboard should go relative to the mast, and where to put the mast itself? There is currently a hole for a mast in the middle bench and daggerboard position is close to the back of the boat.

Also, I'm not sure if this is the correct sub forum to put this post.

any help would be greatly appreciated! The boat will be mostly a one person sailed vessel.

I can post photos of the boat in its current state, if its helpful.



thanks!

 

In a dinghy this size, just use the existing locations.
You also have the size of the Rudder, and the size and shape of the Sail to consider. These make a huge contribution to overall balance.
But the whole dagger board/sail location problem, especially using something as simple as a lugsail, is moot, considering that the huge effect your own bodyweight and gear has.

A reasonable sailing test period its the most fool proof way to work out optimal balance, and often it doesn't have to be as complex as repositioning the centreboard.

 

Pictures would be good. Looks like it should be mast forward daggerboard in the middle.

Davidson D-9 By ShortyPen Sailboat Guide https://www.shortypen.com/?boat=81&d=-Davidson-D-9

 

Welcome to the forum Ocad. Yes this is probably the right place to answer your questions.

You have told us that you are new to boat building and that you want to get into sailing. Good for you,we will encourage you.. While you are still a beginner, you have concluded that a lug rig would be preferable to the standard rig that came with the boat. You have also suggested that you need to move the daggerboard location.

You can probably use a lug rig to put more sail area on the boat than it originally came with. What will be the advantage of doing that? Is it just a matter of a more salty appearance or some other reason?

The elementary design of a reasonably balanced sailboat has the center of effort (CE) of the sail somewhere between 5% and 10% of the waterline length forward of the center of lateral resistance (CLR) of the boat. Here is the deal.......on such a tiny boat the fore and aft trim will move the CLR quite a bit. That means that you can change the feel of the helm by simply moving your weight foreward or aft by just a few centimeters.

My sincerest advice is to leave the boat and it's rig as it was originally designed before changing it. After some sailing time in the boat, you can then determine whether it needs to be redesigned.

Please do not take this commentary as a personal criticism, it is not. We are here for you, please continue.

 

Thanks for all the input. What I forgot to mention is that the boat does not have a sail. All the wood was completely rotted, and we've had to replace nearly everything, transom gunnel, seats, etc. it seems the last owner did a very poor repair job (using nails to attach the the seats from the outside that just ended up rusting, and coins with holes drilled through them for washers, the middle seat has a random hole that it seems they wanted to put a mast in, but the positioning makes no sense. Also it seems they cut a rough hole in the hull for a dagger board. The boat didn't come with a sail, so I am not sure what the rig is meant to be, if it was ever intended to have any.

 

Here is what the boat currently looks like. I've been getting rid of the rotten wood and holes in fiberglass and have gutted it back to this state...

 

Thanks for the pics Ocad.
If it were mine, I would consider molding in the fore and aft seats as air boxes and relocating the middle seat and dagger board case.
Sort of like the front 1/3rd of the white boat above and back 2/3rds of the blue one, but without the side air boxes.
You have accessibility on your side and most likely a lack of rigidity working against you at this point.
I am just an excited amateur working on a couple basket cases myself.

 

Little boats, like the one in the picture, will normally have the mast located very near the bow. Like 10 or 12 inches near. The daggerboard can be found near midships on little boats like this. That is because the sail is pretty small and the CE not far from the mast.

Sure enough, you could adapt the boat to use a lug rig. Lugs are practical for putting a generous amount of sail while using fairly short spars. The word generous is to be taken cautiously. You boat will probably not stand much more than 60 square feet of sail. If you choose to use a marconi style sail then you might want even less sail so as to keep the mast height within reason.

Plenty of work to do to give the boat the ability to sail. Before you do all that work, show us a picture of the boat in profile. It will be useful to see what the curve of the bottom, front to back, looks like. If it is straight back without rising as it approaches the transom, you have a power boat, not a sail boat. You can still make the straight bottomed boat sail but it is not likely to sail as well as a boat with some bottom rocker.

 

Thanks for the advice!
I'm sorry for the quality of the photo, but it's in a pretty cramped workspace, and this is the best angle I could get of the bottom of the hull near the transom. It definitely rises up a bit.

 

Ocad, the picture suggests that there is some rise in the after part of the bottom.

Why have the rise in the rear part of the bottom? There is a legitimate reason. The boat has apparently been designed as a displacement boat. What does displacement imply. The boat moves through the water by pushing water aside. If the transom is not lifted a bit, then it will make a lot of drag as the water becomes turbulent at that location. Getting the transom at or above the water surface reduces the drag somewhat.

Keep up the good work. You have replaced the transom and it appears that you have done a first class job. With enough work I think that you could have serviceable little boat. You are going to need some work to stiffen the gunnels. Simple strips of wood inside and outside will do that suitably well.

Tops said that it will be prudent to install air boxes or other kinds of positive flotation. I heartily agree because the boat in naked form is a sinker.

 

Thanks for the feedback.
I have been completely gutting the boat, and am almost at the point where I've got her back up to a hollow shell (I have had to patch hundreds of holes) so I can almost start building up from there. The gunnel is my next priority. I am a high school student, and have been using my metal shop class as an opportunity to cast brass cleats that I will use on the boat. I was wondering if you have any advice on which type of sail to use. (I was thinking of a lugsail) but I am completely new to sailing, and I have next to no idea.
Thanks!

 

Both those pictures are revealing. The design of boat is better than I first imagined. It does have a conventional rocker curve. It has very rounded chine area that will mitigate drag. The rounded chines will make it a bit more tipsy than a boat with less rounded sections. Not to say that the boat will be too difficult to sail. Once again I urge you to figure out a way to include some kind of flotation. We will help you if needed with that kind of stuff.

Your question about the kind of sail to use, has a variety of answers. Some of the considerations involve; where you get the sail. You could make it yourself, you could shop around for a used sail, or if your budget permits, buy the sail from an established sail loft. A boat of that sort can probably use 40 to 50 square feet of sail. I would consider a simple sprit sail of perhaps 50 sq, ft +/ - . The reason is that the sprit is simple, and has a low center of pressure (CE). and has some adjustment features that are useful. The snotter adjusts the sprit pressure on the peak of the sail. ........... A lug rig will work well enough but the spars are likely to be bigger than the sprit spars. You could possibly find a used Optimist pram sail, a sprit sail, but it is smaller than the size that I have suggested. With a little luck you might find the whole Opti rig including the sail, mast, boom, and sprit. If you live in an area where there is some sailing activity then you are in luck. Otherwise you have to improvise as best you can.

If you can manage to get a professionally made sail, then that is the best option. The ball park price of a new sail is somewhere around five USD per square foot. A price like that might make it a bit expensive for most high school students. That you can make cleats or other hardware, is a good deal. Actually you won't need many solid metal cleats except for mooring or towing use, and maybe for a halyard or outhaul. . You will need about three turning blocks (Pulleys), and hopefully at least one cam cleat. You can improvise all of those if you need to. Really good sail blocks, such as Harkens, are very fancy, highly efficient, and scandalously expensive. You can get by, in the beginning with hardware store awning pulleys. Plan on buying some good quality lines (ropes). Good ones can be a bit pricey too....but they last for a long time.

I have used some words for various parts and mechanisms that you may, or may not have in your working vocabulary. If that is the case, we will be pleased to help you understand what all that jargon means.

Keep up the good work.

 

I had a small boat where I used a 'polytarp' sail for a couple seasons, a Bolger style 'leg-o-mutton' sprit sail (3 corners). The first picture with the yellow sail I enclosed may be one of those.
Instruction can be found online, they can be assembled with all tape or taped and sewn more like a cloth sail (what I did) with carpet tape, a bit of rope, and Dritz grommets from a fabric store.
It would be a way to get sailing and defer sourcing a better sail for the off-season.

 

Hi there,

any further thoughts (after seeing the photos) on whether I should move the daggerboard slot forward? It would obviously make for more work but I want to do it right. If it will make a big difference, I would rather change the location at this point. And if I do move it forward, how do I tell where to move it? Is there a formula for figuring this out? Thanks for any input!

Also, I will definitely incorporate air boxes into my design. Thanks for the great suggestion, Tops!