Stemhead Bow Roller Replacement

Broken Stemhead Bow Roller

A Broken stemhead was noticed during a routine inspection of the forestay toggles.  The stemhead exhibited two long crakes between the mounting bolts on one side and the center forestay/chainplate mounts on the other. This effectively meant that  rigging was only secured by half of the bolts, but worst, the support was through an uneven load.   If left alone, the forestay would likely tear itself out causing all kinds of havoc.

Close view of crack along the headstay
attachment. 

Crack along right set of bolts

Old Deck/Hull Attachment Bolts

Disconnecting the headstay and the roller furler was straight forward.  Removing the 8 mounting bolts holding the stemhead bow roller to the hull/deck was not so easy.  Access to the mounting nuts located at the bow tip is through the chain locker.  There is inadequate space for using a ratchet socket and even little space for turning a wrench.  It took nearly 4 hours to remove the 8 bolts using a 1/2" flexing ratcheting wrench for all but two bolts.  The box end of the wrench did not fit on 2 of the nuts as the nuts were too close to the hull, these nuts were removed using the open wrench end at a rate of 1/6th turn at a time.    Once all nuts were removed, the stemhead bow roller was easy to lift out. 

Stemhead mounting bolts access via the anchor locker.

Securing the roller furler with a seat
cousin at the hull and lashing near toe
rail, up on a side shroud, and at the lower 
spreader.   A temporary (i.e. several weeks) 
mast support was  done with a removable forestay
and two halyards connected to the bow cleats.

Freeing the stemhead bow roller.

Another view of the old stemhead bow roller.

 New Stemhead Bow Roller Design

I found a company online which advertises the fabrication of custom stemheads.  While the products descriptions were nice and professional, the quoted price for a simple single bow roller stemhead was $1,800-$2,000.    I chose to design my own stemhead bow roller, and I was fortunate and very grateful to have the help from a friend in fabricating the design.    The design uses a 1/2" thick  316 Stainless Steel, all 316 Stainless bolts and hardware, and a commercially available bow roller and bow chocks.   A baseplate thickness of 1/4" and 3/8" were considered, but opted for 1/2" plate as it make a more robust design.  The added thickness also allows more secure beveled mounting of the underside bolts and for tapping and threading the bow roller attachment.  A Windline model AR-3 was used for the bow roller which is rated for anchors up to 60 lbs.  For bow chocks,  Schaefer XCL model 60-50 were used.  These bow chocks are secured from underneath the base plate with flush flat head bolts giving the appearance of a nice custom look.  The center chainplate mounting brackets were also bolted from the plate bottom with 4 bolts tapped into each bracket side.  These bolts were thread locked with Loctit 421 and sealed with Loctite PL Marine sealant.  The new design extends the anchor roller out an additional 5 inches but maintains the same winch chain centerline alignment.  This design include space to allow for the addition of a second anchor roller if future needs dictate, but currently plans are leading towards adding a padeye for external asym downhaul  block attachment.   The bow chocks were aligned centered to the chainplate clevis pin hole similar to the original.  The cost in added weight of the new design is an extra 17 lbs compared to the old stemhead bow roller.  This is a small amount compared to my 44 lbs Vulcan and 150' of 5/16" HT G4 chain. 

Before finalizing the design dimensions, a plywood template was made.  The original mounting holes were transferred from the old stemhead and a test fit on the vessel confirmed all dimensions and fitting.  In mounting the new stemhead, nearly a whole tube of Loctit PL Marine was used, much of the sealant was needed to fill a void right at the bow tip where the same amount of old sealant was removed.  The outside seal between the bottom of the new stemhead and the hull topside was made using bead of white Dow 795 silicone building sealant.  

New Stemhead design plan. Base plate is made from 1/2" thick  316 Stainless Steel plate.   The
new design extends the anchor roller by an additional 5 inches but maintains the same winch
centerline alignment.  The design include space to allow for the addition of a second anchor
roller. 

Material List

• Base plate
• 316 Stainless Steel plate  (Online Metals)
• • 316 1/2” x 12-3/4” x 17-3/4"      
  • • includes material for stay mount brackets
• Mounting Hardware (McMaster-Carr)
•  Forestay brackets
• 316 Stainless Steel Hex Drive Flat Head Screw, 5/16"-18, 1" length 
•  quantity : 8  
• Mounting bolts  
• quantity: 8  
• 316 Stainless Steel Hex Drive Flat Head Screw, 5/16"-18, 3" length
• 316 Stainless Steel Hex Nut, 5/16"-18
• 316 Stainless Steel Lock Washer, 5/16"-18
• 316 Stainless Steel Washer, Oversized, 5/16" Screw Size, 0.344" ID
• two bolts used standard 316 Stainless Steel Washers
• Bow chock bolts
• 316 Stainless Steel Hex Drive Flat Head Screw,  M12 x 1.75mm Thread, 30mm Long
• quantity: 4
• Bow roller bolts
• 316 Stainless Steel Button Head Hex Drive Screws 3/8"-16 3/4"
• quantity: 5
• bolts shortened to 5/8"
• Bow Chocks 
• Schaefer XCL Model 60-50 (Marui Pro)
• Bow Roller
• Windline Model AR-3  (Ebay)
• Bolt thread lock & sealing
• Loctite 241 thread lock
• Loctite PL Marine FC adhesive sealant  (a Polyether like 3M 4000UV)
• Dow 795 Sealant, white

 A plywood prototype was constructed with bolt holes transferred
from the original stemhead to test mounting and finalize design.

Old stemhead next to new stemhead. The new designs extends
the anchor roller an additional 5".  

Mounting of the new stemhead bow roller.

New stemhead bow roller with forestay rigged in place.

New stemhead with anchor. A 316T stainless steel boom loop
was added to function as an anchor containment loop.

New stemhead with anchor