All, Crackerjack's genset, a 6kva Northern Lights unit in a sound proof enclosure sits on a synthetic shelf spanning about 40" between the inside walls of one of her hulls. The ends of this shelf sit on cleats glued and screwed to the hull and the ends of the shelf are also glassed to the hull.  The generator sits on 2 supports on each the front and the back each at about the third points of the shelf.  Over the 8 years since she was built the shelf has gradually sagged.  The material seems to have gradually creeped/crept.  There is no sign of distress at the shelf attachment points to the hull. I intend   strengthen the shelf by attaching a 3"x4"x3/8" aluminum angle to the front and back of the shelf spanning the width of the shelf.  The ends of the angle will not be supported vertically.  The 4" legs of the angle will go underneath the shelf and the 3" legs will extend vertically up in front and back of the shelf.   I need to minimize projection below the shelf since access under it to the genset battery and rudder post is already tight. The angle will be through bolted to the shelf with 6 3/8" bolts through the shelf.  I will use bolts with only a smooth shank going through the synthetic board.  I need to somehow glue the 4" leg to the underside of the synthetic board too so that shear loads can be transferred between the angle and the board.  The board is not real hard.  SO I cannot squeeze the bolts real tight and the glue needs to carry part of the load. I considered 3M5200, but it seems to not be very strong for this kind of service and I expect it will also gradually creep.  I guess that leaves me with epoxy.  The plan would be to wipe the angle and the shelf well with acetone to clean it.  Then rough it up with a course sandpaper.  Then wipe it clean again with acetone.  LEt it dry thoroughly and then smear a thick coat of epoxy onto the angle leg and put some inside the bolt holes and bolt the angle into place.  I will leave the temporary shelf support in place for a week or two until the epoxy is fully cured.  I will need a working time of about 30 minutes to get all the bolts in and tightened. Can any of you comment on the suitability of using epoxy for this, suggest a better alternate, and/or recommend a specific epoxy product to use?  My experience with fiberglass is 0 and my experience with epoxy consists of using the small siamesed  plunger tubes in various applications with good success. Gary Hagstrom Iron River, Wisconsin

Wow! 3x4x3/8 sounds like something you'd use for mounting a propulsion engine. Was it Larry Brown who said "there's no doin' like an over-doin'"? <G> I'd concur with your 5200 assessment, but I'd lean toward possibly replacing the shelf or supplementing it with a more rigid material with a honeycomb core. Some of that stuff is exceptionally rigid. Then again, even if the material has sagged to some degree, is it really compromised structurally, or more that it's cosmetic and just bothersome? I've bonded aluminum with West System, there are other epoxy products used in the aerospace industry that are probably better suited do bonding aluminum. If you provide the mechanical tooth as you propose, given the surface area of the piece you're adding, clamping it for the period it takes to fully cure should preclude the need for mechanical fasteners. I'd at least use aluminum fasteners if you do that as opposed to stainless given the way the two interact in the marine environment. Once the epoxy cures the fasteners would be redundant. I'd be inclined to jack up the genset, clean the surface and slide a second piece of cored material on top with thickened epoxy in between; clamp & cure.  Now if the shelf material is some sort of polyethylene, all bets are off getting anything to bond to it. Sounds like an interesting project! ------- Steve Sipe MTOA #3962 Solo 4303 /Maerin / Lying Little Bay, Great Guana Cay Exumas On 3/22/2018 12:16 PM, Gary Hagstrom via Trawlers-and-Trawlering wrote: > All, > > Crackerjack's genset, a 6kva Northern Lights unit in a sound proof enclosure sits on a synthetic shelf spanning about 40" between the inside walls of one of her hulls. The ends of this shelf sit on cleats glued and screwed to the hull and the ends of the shelf are also glassed to the hull.  The generator sits on 2 supports on each the front and the back each at about the third points of the shelf.  Over the 8 years since she was built the shelf has gradually sagged.  The material seems to have gradually creeped/crept.  There is no sign of distress at the shelf attachment points to the hull. > > I intend   strengthen the shelf by attaching a 3"x4"x3/8" aluminum angle to the front and back of the shelf spanning the width of the shelf.  The ends of the angle will not be supported vertically.  The 4" legs of the angle will go underneath the shelf and the 3" legs will extend vertically up in front and back of the shelf.   I need to minimize projection below the shelf since access under it to the genset battery and rudder post is already tight. > > The angle will be through bolted to the shelf with 6 3/8" bolts through the shelf.  I will use bolts with only a smooth shank going through the synthetic board.  I need to somehow glue the 4" leg to the underside of the synthetic board too so that shear loads can be transferred between the angle and the board.  The board is not real hard.  SO I cannot squeeze the bolts real tight and the glue needs to carry part of the load. > > I considered 3M5200, but it seems to not be very strong for this kind of service and I expect it will also gradually creep.  I guess that leaves me with epoxy.  The plan would be to wipe the angle and the shelf well with acetone to clean it.  Then rough it up with a course sandpaper.  Then wipe it clean again with acetone.  LEt it dry thoroughly and then smear a thick coat of epoxy onto the angle leg and put some inside the bolt holes and bolt the angle into place.  I will leave the temporary shelf support in place for a week or two until the epoxy is fully cured.  I will need a working time of about 30 minutes to get all the bolts in and tightened. > > Can any of you comment on the suitability of using epoxy for this, suggest a better alternate, and/or recommend a specific epoxy product to use?  My experience with fiberglass is 0 and my experience with epoxy consists of using the small siamesed  plunger tubes in various applications with good success. > > > > Gary Hagstrom > > Iron River, Wisconsin > > _______________________________________________ > http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com > > To unsubscribe or modify your subscription options (get password, change email address, etc) go to: http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com > Trawlers & Trawlering and T&T are trademarks of Water World > Productions. Unauthorized use is prohibited. > >

Steve is correct. If polyethylene you must use mechanical fasteners to attach the stiffing braces. If you can remove the board you can heat plastic weld additional material .. but mechanical fasteners with washers or plates would draw it straight again especially if you carefully heat the shelf. Again, if a starboard like material(polyethylene). Foam cored “boat board” can be chemically bonded (pvc glue) however isn’t very strong. Good luck! Joe Pica 10031 windward Dr. New Bern, NC 28560 H 252-631-1097 C 301-904-9122 M/V Carolyn Ann GH N-37 http://carolynann-n37.blogspot.com/ MTOA#3813, AGLCA #5485 Platinum Yacht Sales @ Curtis Stokes & Associates joe@CurtisStokes.net

Gary, my thoughts are that what you are planning would work, but one suggestion. Pot the fasteners in the shelf; this will provide a compression post allowing you to tighten down on those bolts that go through the "soft" shelf. Just in case anyone reading this does not know what "potting a fastener" means- drill a hole oversized, fill with resin, then re-drill for the diameter of the fastener. Also, talk with West Systems Epoxy folks as they have some ideas on epoxy and aluminum. Rudy and Jill Sechez St Augustine, Fl, Northbound ICW BRINEY BUG-a 34' Sail-Assisted Trawler 850-832-7748<div id="DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2"><br /> <table style="border-top: 1px solid #D3D4DE;"> <tr> <td style="width: 55px; padding-top: 13px;"><a href="http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail" target="_blank"><img src="https://ipmcdn.avast.com/images/icons/icon-envelope-tick-green-avg-v1.png" alt="" width="46" height="29" style="width: 46px; height: 29px;" /></a></td> <td style="width: 470px; padding-top: 12px; color: #41424e; font-size: 13px; font-family: Arial, Helvetica, sans-serif; line-height: 18px;">Virus-free. <a href="http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail" target="_blank" style="color: #4453ea;">www.avg.com</a> </td> </tr> </table><a href="#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2" width="1" height="1"></a></div>