Improving the design of a Hartley TS21

[jumbuck]

Hi all,

We are about to have another stab at building a Hartley TS21. The first ended in ashes - very sad and painful story, won't bore you.

I am seriously thinking about replacing the 50 year old boilerplate swing keel design with a modern drop down weighted foil shape centreboard - as can be found on almost all recent trailer sailers.

Do people suggest I simply emulate the exact surface area of the boiler plate but just go deeper, which would mean it would end up slightly thinner?

We are building the Hartley TS21 to commemorate 50 years of the trailer sailer just in case people think I have rocks in my head wanting to build such an old boat. However, we are considering a variety of minor design modifications to improve her whilst not wanting to venture too far away from the original well proven design.

Any thoughts or suggestions would be very much appreciated.

Thank you

[Doug Lord]

Would the new keel modifications be class legal for racing-and does that matter? If you lower the CG of the keel you are increasing righting moment and you'll need to take a close look at the boat structure and rig design to be sure everything can handle the increased loads. Have others in the class made similar mods?
Good Luck!

[jumbuck]

Hello Doug,

Thank you for your reply Doug.

Class legal is not a concern to us. We know we are going to be outside the official measurement anyway and so during the first group of meets we may be able to have her own CBH rating established.

Due to the age of the design (near 50 years) there have been a wide variety of modifications made by owner/builders over the years as they attempt to incorporate modern building techniques and changes to boost performance. I've studied may of these and some of them are pretty aggressive while others are discrete but highly effective.

On one the owner built the boat with a slightly flatter under waterline hull shape, and according to the owner it has put his boat in another class as far as performance goes. He describes his boat as having "slightly less of a banana shape underwater". He also has bowsprit and asymmetric spinnaker.

On another they have built in a weighted foil shape drop down centreboard instead of the swig keel plate, which also is reported to have made a substantial improvement in overall performance.

At the end of the day she will not be a true Hartley TS21 but the exercise to study what can be done to improve her by design has huge potential to bring performance benefits ... if done very carefully. Are there any areas where you would suggest improvements can be made?

Cheers

[Doug Lord]

Originally Posted by jumbuck

Hello Doug,

At the end of the day she will not be a true Hartley TS21 but the exercise to study what can be done to improve her by design has huge potential to bring performance benefits ... if done very carefully. Are there any areas where you would suggest improvements can be made?Cheers

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As long as the structural implications are taken care of properly-possibly with the assistance of an NA or proven work by another owner I'd go with a deeper vertically lifting bulb keel and with rig improvements such as a square top main, if possible and desirable. If the RM is increased it would probably pay to increase the SA to take advantage of the greater power to carry sail.
It sounds like it could be a fun project as long as the structural requirements of any changes are meticulously dealt with.

For those not familiar with the boat: http://mytrailersailer.com/hartley-ts21.html

[Petros]

I think that is a great idea, as long as the boat you build give you want you want. It is a lot work to build a boat, so make sure it suits your needs before you get started.

I see nothing at all wrong with updating the keel or any other part of the design. However, as pointed out, if these are regularly races you would not have a handicap rating for your altered design.

Make sure you approach the alterations carefully so you do not end up with something difficult or dangerous to operate.

[jumbuck]

Thank you Doug and Petros for your replies, much appreciated.

Can I ask what RM and SA refer to please Doug.

I like the idea of moulding the lead as part of the actual foil at the bottom of the drop down centreboard, i.e., top 70% wood, bottom 30% lead. That way she can be raised completely.

These boats must have around 250KG ballast and the plan states this is to be on the floor beside or in front of the centerboard case. Imagine how much more efficient it will be when the bulk of this ballast can be positioned at the bottom of the drop down centreboard.

Best regards

Peter

[Doug Lord]

Originally Posted by jumbuck

Thank you Doug and Petros for your replies, much appreciated.

Can I ask what RM and SA refer to please Doug. Peter

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My apologies-wasn't thinking: RM= Righting Moment ; SA= Sail Area

Peter, could you change the cabin configuration to a flush deck or raised flush deck? advantages: more deck space, more interior "roominess", better aerodynamics.

pix=raised flush deck-click on image:

[jumbuck]

Hi Doug,

Thanks for your reply Doug.

Yep, current plan is to increase freeboard by about 80mm and reduce cabin top height accordingly but we'll stick with having a cabin as this keeps the boat at least along the lines of the original design. I'm hoping she will still clearly be recognisable as a Hartley TS21 - although what goes on under the waterline is a different thing.

I'm going to build a 10% model of her which will be sort of therapy for me (after the fire) until I can get started on building this second one in earnest.
Cheers for now

Peter

[Gary Baigent]

My friend Jimmy Keogh has a modified Hartley 18; he extended the stern with a small scoop, cut the cabin in half, lengthened cockpit, made a new daggerboard and rudder ... and took all the ballast out. The 18 is a dinghy anyway and as Greg Elliott says, "ballast just dumbs the boat down" - or words pretty close to that effect. Jim thinks he may need a little internal ballast forward to keep the buoyant bow down in a seaway.
When you disregard, or remove, the ugly dog box, the Hartley hulls are okay ... and provide plenty of fun sailing at little expense. Ho on, be a devil, make your 21 into a true dinghy too.