Sailing - Adding a bulb to the keel

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Adding a bulb to the keel

Printed From: Laser 28 International Class Association
Category: Laser 28 General
Forum Name: Sailing
Forum Description: Everything on sailing the boat
URL: http://www.laser28.org/forum/forum_posts.asp?TID=78
Printed Date: 23 November 2024 at 1:54am
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Topic: Adding a bulb to the keel

Posted By: tonycooke
Subject: Adding a bulb to the keel
Date Posted: 01 November 2004 at 5:58pm

Hi, here's another question to make the "keep it strictly standard" folks mad!

I'm considering adding a small (200 lb.) bulb to my keel, about 4 inches up from the bottom. The reasons? I often sail single handed; when I race in phrf I rarely have more than four guys aboard (including me); I teach the CYA basic Cruising Standard on this boat, with a maximum of 4 students aboard and more usually 3 or even 2. I sail on Lake Okanagan in BC where big gusts and rapid wind direction changes are commonplace. In all of these conditions I find the boat to be a bit too tender.

I've had some positive feedback on this idea from Mike Demuth who fitted a similar bulb to his boat 12 years ago, but would greatly appreciate any other opinions before I order a bulb from Mars Metal.

Will the extra keel weight over-stress the rigging? Will a small bulb noticeably stiffen the boat? What will be the overall effect on performance?

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tony cooke

Replies:

Posted By: Guests
Date Posted: 08 November 2004 at 3:11pm

Tony,

I have gone through the same process as you and went as far as having Mars draw up some plans for a extension with bulb.

A friend of mine (who is a boat builder) reminded me of the reasons I like the boat. It flies off the breeze. One reason for this is the small fins....

I too had got to the point where I was looking for more stability, however I think you will find it is more about depowering the sail plan than adding weight and drag to the keel.

My wife and I cruise the boat in breeze (>30) with just a working jib up... very controllable. Also consider a third reef and slugs for your main for short handed sailing.

Posted By: tonycooke
Date Posted: 09 November 2004 at 12:40am

Thanks for your thoughts Chris. Your comment about the boat's off wind performance strikes a chord with me, I bought a Laser partly because of its ability to surf and plane. I'd hate to lose that planing ability. I'm also a dinghy sailor (JY15) and I'm addicted to the rush you get when you are reaching on a full plane!

I've sailed several times singlehanded with jib alone in a decent breeze and I concur that the boat performs surprisingly well in these conditions.

This is my first year with a Laser 28 but I learned early on that to be competitive in phrf the boat needs LOTS of crew weight.

I just thought that a couple of hundred pounds on the keel was no more than one extra crew member on the rail as far as weight was concerned, but far more effective in terms of keeping the boat on its feet. There is the question of drag though as you rightly mention. Having said that, most of the modern high performance boats have bulbs and they have no shortage of speed. I realise they were designed from the outset with a bulb as part of the plan. I wish I could assess the drag that a small bulb would add.

Regards

Tony Cooke

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tony cooke

Posted By: khardy
Date Posted: 10 November 2004 at 10:37am

“… a couple of hundred pounds on the keel was no more than one extra crew member on the rail as far as weight was concerned, but far more effective in terms of keeping the boat on its feet.” Not true; adding the equivalent weight of one extra person to the bottom of the keel is far less effective at keeping the boat on its feet.

Crew weight is far more effective, per pound, than weight in the keel. The quantity you want to increase is called “righting moment” which acts to oppose “heeling moment.” But the keel generates no righting moment until the boat begins to heel. Further, the amount of righting moment generated by the keel increases as the boat heels. But the crew adds righting moment any time it moves out on the rail.

Not withstanding crew weight, your two options for increasing righting moment are some combination of adding weight to the keel, or lowering the weight you already have. I doubt that adding a bulb will add much drag. But, I also suspect you’ll get minimum improvement at a maximum price. If you really want to modify the keel you might consider making the keel longer by lowering it. You could remove the keel and add a longer “base” for it to bolt too. Then re-attach it and fair it in. You’ll have to work out a way to lengthen the keel bolts like welding extensions to them. This may be more expensive than a bulb but I think it would be more effective at solving your problem than a bulb. It has the advantage of adding righting moment without adding significant weight. Also, with a deeper keel you’ll increase the up-wind performance (though at the expense of downwind performance.)

Keep in mind that such a modification is likely to adversely impact the re-sale value of the boat. Also, the structure of the hull wasn’t designed for this added weight. I concur that the cheapest / easiest way to solve your problem is to simply shorten sail. Maybe have a main re-cut at the first reef?

Ken
Tenacity 241

Posted By: Guests
Date Posted: 29 January 2005 at 10:39am

Instead of a bulb, you might consider sailing the laser 28 in it's original configuration. That being a 3 sail boat. Main, 100% jib & spinnaker. When my family & I 1st sailed our boat with a 150% genoa we thought at 1st "wow what a skidish boat!". Then we talked to the Bruce Farr office & they reminded me that the boat was originally designed as a 3 sail boat. The genoa tracks were installed so people could enjoy the boat in PHRF until a class got established. Well we had Doyle make us a 100% jib (not a #3) & said design the jib like one on Soling or E22 jib. Something good from 0 to 20 kts.

We haven't missed the genoa to date. We sail with myself 2 thirteen year olds & 2 women. Our crew wieght is light & the boat is so much friendlyer to sail.

"good luck"

Comet172

Posted By: Guests
Date Posted: 12 May 2005 at 12:08pm

I sail a laser28 in cape town with a buld keel. We a very competive inthe IRC system. Coming second in Nationals. The boat is very stable and we maintain around 6.0-6.6 knots upwind. We sail often in 30+ knots. downwind is fast and stable.

Posted By: Guests
Date Posted: 23 May 2005 at 6:46pm

I sail in S.F Bay and it is windy, typically 15-25 any afternoon in the summer. I have found that a longer rudder (I had one made)has made a huge difference in boat control. The original rudder was way to short and would come ungluded with just the least amount of excess pressure in a puff or mistake by a trimmer either upwind or downwind. Cost for a new rudder is about $1,500 or $2,000 for a carbon shaft. The new rudder doesn't add to wetted surface or weight in the back of the boat either and sure make a difference in rough and windy condiitons.

Good Luck
John Davis

Posted By: Guests
Date Posted: 23 May 2005 at 6:48pm

I sail in S.F Bay and it is windy, typically 15-25 any afternoon in the summer. I have found that a longer rudder (I had one made)has made a huge difference in boat control. The original rudder was way to short and would come ungluded with just the least amount of excess pressure in a puff or mistake by a trimmer either upwind or downwind. Cost for a new rudder is about $1,500 or $2,000 for a carbon shaft. The new rudder doesn't add to wetted surface or weight in the back of the boat either and sure makes a difference in rough and windy condiitons.

Good Luck
John Davis

Posted By: Guests
Date Posted: 24 June 2005 at 1:39am

Tony,

My father added a 400 lb bulb, designed by Farr, to his Laser 28, for the same reasons you state. Farr said the boat, rig, etc. could take the loads. It slows us down a bit down wind, but we can sail short handed to weather and not experience the slow-down-in-a-gust syndrome. Of course, sailing short handed down wind we weigh about the same as a fully crewed boat without a bulb. A friend in So. Africa also added a bulb, mainly because it blows so frightfully hard there. He had to do some structural repair to the structural grid, but that was after a long slog to weather in 45-60 kts!

Posted By: Guests
Date Posted: 09 November 2005 at 5:19am

We actually won the race in the 45-60kts that we saw that day on corrected time (irc).We were racing alot bigger and heavier boats.

Hadding the keel has made us very competive in the local irc fleet We won the single handed and double handed races last year both sailed in 25 - 35 knots. racing against a first 47.7

If racing on handicap i think it helps the boat alot. We a re still very fast in light air as well.

Posted By: Guests
Date Posted: 01 December 2005 at 12:26pm

I've been sailing a Laser 28 for a season now here in the UK and I've learned to love its downwind performance.

In my opinion adding a bulb would increase the righting moment and also increase drag, which is not good for downwind sailing as we all know. As khardy says the righting moment acts to counteract the heeling moment, hence the other option could be to reduce the heeling moment. This could be done by lowering the centre of effort of the mainsail for example. If the sails were simply modified in section shape and not area this would have minimal effect downwind where it is the drag of the sails that is mainly driving the boat.