Going Up and Down – Part 2

Since I first posted details on the Sage 15 daggerboard (yes it was a few months ago) I’ve personally put in over 30 hours of sailing in the Sage 15 sloop and catboat (aka, SageCat).  The daggerboard is providing exceptional righting moment and the boats, like their big sister the Sage 17, hit a ‘wall’ and don’t like to heal more, and when the wind blows the S15 and SageCat don’t ‘tip’ like a small 750# ‘dinghy sized’ craft.

Building a small daggerboard pocket cruiser, meaning a boat with a cabin where two adults can sit and sleep, isn’t something many manufactures have attempted.  There are larger centerboard cruisers such as the Sandpiper 565, Potter 19, Seaward’s boats and the Hobie 33.

The Sage 15 daggerboard is different than most other boats:

  • angled aft
  • has 225# of lead in the bulb
  • when down the daggerboard doesn’t intrude the cabin space as the trunk is under the v-berth.

The above differences do present design challenges and it is these that I’ll detail in the this post.

As the board is angled aft the raising mechanism needs to allow for the daggerboard’s weight not being in-line, meaning straight down, as the board moves up and down.  The balancing point needed to be determined so the board didn’t bind in the trunk when being lowered/raised.  In addition the corresponding pull point on the cabin roof needed to be located.

Inside the daggerboard trunk are guides that hold the board in place and keep it from rocking front-to-back and side-to-side.  We call these guides ‘bearings’ as they also take the weight and forces of the daggerboard as the boat heels.  As the board is angled, front-to-back, the bearing design must account for the board moving in two planes … not just straight up, but front-to-back.

IMG_20160805_150952736_HDR

ASOLARE’s daggerboard in the down position.

If it is so challenging to design a boat with a keel angled aft why go to all this trouble?  Two reasons:

  • The boat’s sail center of effort is slightly aft of the v-berth.  If the board went straight up and down there would not be a good sized space inside the companionway to stand, use the potti, or put one’s feet when sitting on the cabin seats.
  • The angled keel will naturally shed kelp, weeds or other items that come across the leading edge.  The angle is just right so as the boat moves forward kelp will move down and off the bottom of the board.

 

Yes a daggerboard results in there being a ‘hole’ in the middle of the boat that can result in water coming into the cabin.  There are bearings at the top and bottom of the trunk.   These bearings combat water splashing into the boat because they are also baffles that reduce splashing inside the trunk.  To combat water from going between the bearing and board when sailing in very heavy seas there will be a seal the top of the truck incorporated into the v-berth cushion insert.  The top of the cushion will be a couple of inches of foam and a fabric covering so the crew can comfortably  use the entirety of the v-berth.  The bottom of the insert will have a seal so any water that gets past the top trunk bearing will not get into the cabin.

prototype S15 top daggerboard trunk bearing

Prototype S15 top of trunk daggerboard bearing. NOTE: The daggerboard photoed doesn’t have its insert yet. Production boats will have an insert in the top of the board that keeps one from dropping items into the daggerboard … like keys and a cell phone.

With 225# of lead in the bulb of the daggerboard, and the fiberglass structure of the board, the overall weight is about 250#.  This structure provides excellent ballast and the boat really stands up well once she heels over about 10 degrees.  Now how do you raise this weight?  A pennant line (the red line in the above picture) runs from the top of the board to the cabin top, turns starboard to a cheek block and then runs aft though seven blocks set in a cascade.  The line then exits the cabin’s aft bulkhead and turns forward to a #6 winch on the cabin top.  The boats come standard with a 10″ winch handle.  Overall the blocks, winch and handle provide a 13:1 mechanical advantage.  This means that at the winch you are lifting about 19 pounds.

A daggerboard needs to be locked in place to assure it doesn’t slide into the cabin if the boat experiences a knockdown.  Once the board is down it is locked in place with two bolts.

An acknowledged concern is ‘what happens if you hit bottom when the board is down’?  The Sage 15 daggerboard is swept aft.  If the board hits and obstruction the boat will lift up and dissipate the energy of the impact.  As noted above the board is locked in the trunk with bearings.  The bearings will transfer the energy of an impact to the trunk.  The truck is bonded to the hull, a forward bulkhead and the the aft bulkhead of the v-berth.  These two bulkheads are fully bonded to the hull and the berth structure.  Yes, the daggerboard trunk is very strong.

daggerboard trunk and bulkhead in place

The daggerboard trunk and forward bulkhead bonded in place.

The next post on the Sage 15’s daggerboard will detail sailing and cruising differences v. the fixed keel or shoal keel/centerboard setup.

4 thoughts on “Going Up and Down – Part 2

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