banner
Site Feedback  |  Login  |  Terms of Use  |  Search:
Story/Technical Portrait Image

M17 Top Down Furling Asymmetrical Spinnaker with removeable Bowsprit   Total Page Hits: 685

Post Type: Technical/Project

Boat Part: Spinnaker

Date Modified: 03/17/2018 9:12 PM

Details

Serenity is equipped with a semi-retractable/removable bowsprit that sits out 30 inches in front of the bow, allowing a top down furler with a spinnaker to be placed well in front of the head stay and jib.

The bowsprit is constructed from a 5 ft piece of heavy gauge 1.75 inch diameter aluminum tube with 0.120 inch wall thickness secured by passing through two brackets that are fixed to the deck.

The bowsprit brackets are constructed from 2 x 2 x.120 inch square stainless steel tubing that are cut to be 2 inches long.

The first bracket is welded to a larger 1/8 inch stainless steel stem head plate mounted and patterned to fit underneath the M17 factory stem head plate. The plate is secured via the standard M17 stem plate bolt holes plus 2 additional stainless bolts in line along the deck/hull fitting. The through bolts from both the factory stem head and the extension plate are re-enforced by two 6 inch 1/2 x 3/8 aluminum bar tucked on the underside of the deck hull joint on both side of the bow.

The second bowsprit bracket is mounted on the deck 30 inches back from the bow on top of a teak block with with a 4x4 inch square 1/8 stainless backing plate inside the cabin.

The bowsprit passes just to the port side of the stem head on the bow, and is adjusted to be dead centre with the bow at the tip of the bowsprit. The bowsprit is installed by sliding it through the brackets and is secured with two 1/4 stainless eye bolts. A bobstay is fitted from the end of the bowsprit to the boat's Stem Eye. It is fashioned from standard 1/8 stainless rigging cable complete with snap shackle and turnbuckle for tensioning.

A Seldon gx7.5 top down furler is attached to the tack of the bowsprit with the furling torsion line being hoisted by the re-purposed jib halyard that was freed up when the boat received it's CDI jib furler. The line is lightly tensioned using the port side jib winch on the cabin top.

An attachable masthead assembly positions the spinnaker torsion line approximately 5 inches forward of the forestay at the masthead. (see Serenity's other post on the removable masthead assembly)

A custom dimensioned Asymmetrical A3 spinnaker was designed and made in the Seattle loft of Quantum Sails. It was cut a touch flatter and somewhat higher to reduce sail area providing a 216 sq ft Asym with slightly better upwind pointing performance than a conventional A3.

The continuous furling line for the top down furler has a large 60 series Ronstan block threaded onto the line that is then mounted to a teak block attached by bungee cord to the port side stern cleat. This keeps the continuous furling line nicely tensioned and easy to use.

There are 2 sets of dual low friction aluminium fairleads also threaded on to the continuous furling line. These are used to to provide a removable fairlead system for routing the continuous furling line down to the cockpit on the port side of the boat.

A low friction aluminium fairlead lashed to a small stainless snap shackle with Dynema is threaded onto each of spinnaker sheets. These are used as turning blocks to return the spinnaker sheet back towards the jib winches.

The spinnaker sheet turning block attachment points were constructed by splitting a 5 inch x 1.5 inch diameter piece of red brass (aka gun metal) in half. These brass mounts are equipped with embedded stainless eye bolts and mounted in line with the teak toe rails about 18 inches behind the jib winches. Each of them are through hole bolted to a 5 inch 1/2 x 3/8 inch aluminium backing bar on the underside of the hull deck joint in a similar fashion to the stem plate mounting arrangement previously described.

The whole setup works like a dream... Sailing single handed the majority of the time, I can rapidly deploy or furl the spinnaker without ever having to leave the cockpit... The gap between the spinnaker and the head sail is sufficient to allow gybing on the inside.

If I was to do it again the only change I would make is to use Selden's newer CX furler which allows a similar torsion rope deployment for use with a code 0/A0 or other upwind drifter, and then use their cx to gx adapter when flying a spinnaker... Thus allowing one furler to support deployment of either a drifter or a spinnaker.

A final comment.. This spinnaker configuration is a lot of sail. It works great up to about 10-12 knots or so on a broad reach with it’s sweet spot being about 8-10 knots on the M17 for lazy sailing. After that as one might expect the boat becomes markedly over powered and its time to furl it up.

Photos

Post Image
Post Image
Post Image
Post Image
Post Image
Post Image
Post Image
Post Image
Post Image
Post Image
Post Image