Cores/Decks/Loads
Ross;The failure of balsa core decks in some areas on Seidelmann yachts is a function of poor bedding/ construction techniques in areas of fastners/hatches/ports/travelers/and ANY hole drilled into the deck.I have laid up over 80 decks in my career and in the old days( '80-'81-'82-'83) not much thought was given to the migration of water into the balsa[wood] areas.In the case of my 34('82), there was not one place where the balsa core was cut back 1/2" and a putty of epoxy put into the edge.In later years of boat building we realized that a plywood insert at the area of a port/hatch /etc. AND the proper sealing of that wood PLUS the correct bedding compound could help to eliminate the kinds of problems I found in RogueWave.Every port was cut out with no more than a sealant placed between the port and the (wood) balsa core.Over time, you will find that water intrusion begins to "rot" the edges of the end grain balsa.On RogueWave I found every thru the deck placement was done to old standards.Today, each drill hole into the deck area should be enlarged and epoxy pumped into that area to form a solid plug.Then if you drill thru ,you expose no core material, and with a good beddding compound you seal the epxoy fillet and there is no chance of water getting into the core. In the days that the Seidelmann yachts were laid up many yacht buiders had not addressed these problems.Some of the more advanced manufactors began to put indexed placement of wood/ or aluminium / or solid glass plates to help seal these areas.To answer your question: any dense material...wood/aluminum/FRP plate , properly prepped and sealed will carry the compression loads. In the case of high loads...ie- travelers, we used an aluminum plate coated with polyester resin , and then bedded into core-bond to handle the types of loads seen in winches/tracks/travelers.Standard plywood(exterior grade or better) sealed with epoxy ,depending on the thickness, is a very good core in some areas.If a thin wood is used, then a backing plate is best, but in some applications a fender washer is ok....this is a function of the material + the thickness+ the load.For example: if you have a 1/2" ply in a high load area of the lifting nature, that may have too little thiness without a good aluminum backing plate. When we talk about compression loads, mainly we are dealing with the compression of screws holding down some type of fitting...ie-stanchions.Stanchions are in the static position under compression from the very hardware which attaches them to the deck.However, they also, will come under sheer loads(side) and in some cases upward loads(lifting) if lines are lead under the life lines in a fouled line situation.Crew members boarding by grabbing the life lines is one of the loads which work the base of the stanchion until a break in the bedding coumpound causes failure of the seal.If you have a solid base..ie, glass, epoxy,wood sealed in WEST, them the problems are not as great. Seidelmann owners are finding that many short cuts where taken in the building proscess......as did many other builders from that day.Today we can repair almost any type of problem with the excellent choice of state of the art materials we have available .When using a core material, be sure to place a solid plate in the area of extreme loading.Hope this is a help??.As always I can be reached at 904-349-6872 for any consultations...no charge to any Seidelmann owners.Fair Winds & Following Seas:Capt.HawkRogueWave-S34 custom offshore