Would adding .5 metre to keel be worth it?

[brightontrader]

Been thinking about this for a while, interested in opinions.

Yacht is steel 46 foot fin keel sloop with in mast, very tall one and pilot house, so a lot of topsides.

Is tender and in marina with a strong side on blow can list 10 degrees or more. Have to reef going upwind in an early 4, she carries a huge yankee so in stronger winds roll this up and leave self tacking staysail fully out.

Draws only 1.8Metres (6 foot), has 7 ton of lead in keel, boat displaces 20 tons apprx.

My previous yacht drew 2.3M and I had no issues with that really over 14 years of long distance stuff. (but skipped Cuba and Bahamas partially because of draft). Yacht is Dutch built and a lot of their designs have this draft so can sail inland waters locally. Is now based in Brighton UK but will be sailing mainly European waters, no plans for further afield currently.

I have been wondering if welding on half a metre of keel and dropping lead lower, keeping the weight overall the same would stiffen the boat enough to make the work worthwhile. (don't think its a huge job on a steel boat.)

I am told that stability is more about the ballast weight than where it is placed.

any views appreciated:

[denverd0n]

Well, since you asked, here's my view...

A boat is not a series of independent elements that are just slapped together. Choose a hull from column A, a keel from column B, a mast and rigging from column C, put them all together however you want and you end up with a seaworthy boat. No, it is a whole system. Everything works together. Everything is designed to function as a whole. Change one thing and it affects everything else in various and sundry ways.

If you are not a qualified naval architect, capable of doing all the many engineering calculations (and obviously you are not) then how are you going to know all the many ways that extending the keel is going to effect the boat? Answer: you won't.

So, you have two options as I see it. 1) You can roll the dice, give it a try, and hope that you don't completely ruin a perfectly good boat in the process. 2) You can engage a qualified naval architect, or perhaps better yet, consult with the original designer of your boat, and get some expert advice before doing this.

Good luck, whatever you do.

[GordMay]

Check out Mars Keel Technology:
➥ Lead Keel Stability Bulbs | MarsKeel (Production)
➥ Torpedo Bulb Installation Guide | MarsKeel (Production)

[brightontrader]

Yes points taken on naval architect's input, obviously would get this once I have a better idea of how it would affect the boat....., however the original yard and designer are no longer in business not contactable.

When I bought the boat a year ago I had issues with the prop pushing the boat to starboard on over half power so went up this road once already, the naval architect's wanted very large fees to look at the problem, £1000 just to visit the yard, and in the end I solved it with a new smaller prop with more pitch and cutting 6 inches off the shaft after moving the P bracket, taking the prop further away from the rudder, for free.....after advice from various people on this forum.

I did send drawings and this question to 2 yacht builders 9 months ago and got no response, they want to design whole yachts, not keels for existing boats they didn't design.

However thanks for your input. I should have explained this first.

[Dave22q]

I completely understand your frustration. Unless a relative, I doubt if you can find a naval architect to give you a 'quick and dirty' solution. I think the key issue is the moment of inertia or resistance to rotational force. Its a leverage issue so both location and weight matter. It's the same as how 10 lbs in the center of a lever is equal to 5 pounds at the end.
You need to compare alternatives by using a weight based average location from the waterline.
It is necessary to know where the weight is to calculate this. For example going from a uniformly loaded 6' keel to a thinner bulb keel where 1/3-rd of the weight is in the bottom foot will move your weight averaged location from the 3' keel midpoint to 3.8'. That would be roughly equal to the effect of a 28% increase in rotational resistance. Hope this helps a little. Maybe you can find an engineering Professor in a local school to give you a hand. Good luck.

[pcmm]

First thing I think you need to do is find out who the original designer is/was and see if your hull deviated from the design at all. from an uneducated eye, that looks like a small stubby keel for such a mass of boat! who is the designer to begin with?

[brightontrader]

I wish I could contact the designer, like I said in an earlier post, the designer and builder have disappeared....I searched for them extensively with the prop issue.

The chap I bought the boat from was living on it, so there is no address for him either, I had some contact but his english was poor and my dutch is worse, so eventually I didn't get any more responses from emails I sent about wiring and relays etc. (I virtually had to re wire the boat as what was there was far too complicated for ocean going, unless you were some sort of electrical engineer, everything was relayed instead of coming to a bus bar.)

I seem to be getting some good feedback now, for instance, the keel does look a little "stubby" to me too!!

I do have a naval architect mate, he lives in Picton NZ now, once I have some more idea I can get a 1st pass from him, I do have the original plans.

[nortonscove]

It's a steel boat. Find a good welder and have at it. If it doesn't work cut it off and start over. We deal in tug and barge work and welding things where you need them now and removing them later is par for the course. Problem with most people is they have been spoiled by advice from those that talk but don't do. If you were here we'd try that and have it done with inside a couple days whether or not it worked.

[Stumble]

As Denver alluded to changing one major system has cascading effects on the rest of the boat so they need to be done with care.

In this case dropping 7 tons of lead .5m will add roughly 23,000ftlbs of righting moment (max) to the boat. This is a massive increase.

It very well may be doable, but my primary concern is that the rig may not be strong enough to handle the extra RM. Which would entail replacing the mast and standing rigging to handle the new load. The upside is you really don't need a NA to do these calculations, a skilled rigger can run them for you. You may need to do an incline test on the boat first (putting known weights on the deck and measuring heel), but that isn't terribly difficult.

My best case is no mast work needs to be done and you can go right ahead with this. Worst case the boat would need a new mast to handle the new RM.


I would also add two things...
1)having a new keel made is likely an easier and cheaper route than trying to add an extension.
2) the keel you have looks to me like it is shorter than the original design. I don't remember ever seeing a keel that was shallower than the rudder. So I have hope this would be a simple bolt on job that wouldn't need new rigging.

For the detailed view get a copy of 'The complete riggers apprentice' by Brion Toss. Heck you could call Toss and ask his opinion. He is exactly the type of rigger I would recommend to review the job.

[valhalla360]

Yes, deeper will make the boat stiffer. I'm guessing the original keel was per design but a trade off to keep it shallow draft.

In addition to making it stiffer, you need to consider how it affects your sail plan balance. Monos generally want to round up as the downwind sails push forward and the upwind keel creates a backward drag. If you keep it modest, you shouldn't notice a big difference but if you get crazy, it could make a noticable difference.

Honestly, if you can get a nael architecht out for 1000, it's probably a good deal as he should be able to head off any obvious issues.

[Foredeck]

I think Gord May and Stumble's advice will save you time and $ & get you what you need.

I have made a keel mod with Mars Keels and know others who have. These folks really know their stuff.

Concur that trying to insert a section in your keel is going to be perilous and expensive. Adding extension with bulb to the bottom of keel is much easier to do.

Mars will want a lot of numbers to do some calculations for you. Your current ballast to displacement ratio is around 30% and quite shallow. Low 40s & deeper makes a stiffer boat that will likely point a little higher than she does right now, and may make her a little more sea kindly.

Once we had all this worked out for my boat, and Mars poured the add-ons, it was a weekend's work for a team of three to do the job.

As someone said, a keel shorter than rudder is unusual, and creates a lot of vulnerability.

Good luck, and keep us posted.

[ventura 38]

i had an O Day 22 with shoal draft keel. it was very poor up wind. i call O Day at that time they were still in business and talked to there engineers they said to add one foot to the keel and 100LBs it would make it sail better up wind. so i add a foot an one half and 200LBs.to the keel the difference was amazing. i pointed higher could handle bigger wind and waves.

[minaret]

Originally Posted by GordMay

Check out Mars Keel Technology:
➥ Lead Keel Stability Bulbs | MarsKeel (Production)
➥ Torpedo Bulb Installation Guide | MarsKeel (Production)

Have installed a few Mars keel bulb extensions, and in one case they cast a piece for either side that turned the current keel into a bulb without increasing the draft. Simple and the right way to go about it.

[Lokiyawl]

Originally Posted by brightontrader

Been thinking about this for a while, interested in opinions.

Yacht is steel 46 foot fin keel sloop with in mast, very tall one and pilot house, so a lot of topsides.

Is tender and in marina with a strong side on blow can list 10 degrees or more. Have to reef going upwind in an early 4, she carries a huge yankee so in stronger winds roll this up and leave self tacking staysail fully out.

Draws only 1.8Metres (6 foot), has 7 ton of lead in keel, boat displaces 20 tons apprx.

My previous yacht drew 2.3M and I had no issues with that really over 14 years of long distance stuff. (but skipped Cuba and Bahamas partially because of draft). Yacht is Dutch built and a lot of their designs have this draft so can sail inland waters locally. Is now based in Brighton UK but will be sailing mainly European waters, no plans for further afield currently.

I have been wondering if welding on half a metre of keel and dropping lead lower, keeping the weight overall the same would stiffen the boat enough to make the work worthwhile. (don't think its a huge job on a steel boat.)

I am told that stability is more about the ballast weight than where it is placed.

any views appreciated:

You seem to be getting some pretty good advice on your project, I especially liked the response by Stumble. I would also recommend that you do some stability calculations/ simple tests to verify that the spar, rigging and chainplates are able to handle the higher loads generated by a stiffer hull. Just looking at the photo you provided, the fore/aft section of the spar looks pretty massive so if the rigging is matched my guess is that you are probably going to be fine..just check it. Also just from looking at the photo, I would say that the boat will definitely benefit from the addition of more keel in just about every way except for the increased draft and wetted surface. I think that you will end up with a significantly stiffer boat that sails and even handles better even under power since your pivot point will be more solid. (reduced leeway/sliding when turning, ever try to turn a sailing dinghy with the board up? (grin)) One thing that I would suggest is to consider any needed changes to the position of the CLR if needed. Does she have too much weather helm, lee helm? Some or all of that could be potentially dealt with at the same time. You could experiment with the proposed planform by tack welding some temp plates in place, use plywood etc. if you wanted to play around with the design yourself. The bulb keel idea suggested could certainly help you move the ballast and concentrate it as low as possible. Just realize that the motion comfort of the boat will go down as the stiffness goes up but if the boat is so tender that you are avoiding trips, it will be a good trade! Best of luck to you. James

[brightontrader]

Well helpful replies all.

Though not so sure about taking the keel off and starting again. Its part of the hull. Surely much easier to cut the bottom plate off with a grinder and take the lead out, hoping its shot, bend out some 6mm plate and weld on the bottom plate again, add lead ballast. (Sounds simple doesn't it;=)

I used to work offshore on derrick barges for McDermott, admittedly as a diver,( read: underwater cowboy,) but am used to working on steel projects, or more accurately directing them.

I need to take into account extra weight of steel and take it off the ballast weight, and check rigging. On that subject I am an upright sailor, not a sail her on her ear sailor.I would rather reef early and motorsail upwind, if I have to. Its a cruising boat with 1500L deisel tanks and an 83HP 4th sail.

Also I don't think I am going to get much for £1000 from a NA, as I said, the last time I contacted 2 they didn't even reply on this project. The UK has full employment and everyone is busy...certainly in the south where I am. But I am going to have to have pro calcs for sure, just good to know why and what you need before contacting the NAs.