CONTINUOUSWAVE

Give me advice on the exact layup [specifications] and [laminate] construction to use with the two-piece mold seen in Figures 1 and 2 below from an unknown boat mold.





BACKSTORY
I am a boat builder in New Zealand. I have an old two-piece mold for a hull of about 5-meters length. I am not sure on model. I’m considering giving making a hull a go on this mold. It’s in reasonable condition considering its age and it’s been stored outside.

I could guess using gelcoat, polyester resin, and a few layers each side of some foam mat but I’d like to know what’s best.

This forum concentrates on classic-era and modern-era Boston Whaler boats. I don't understand why you are posting here about a hull mold you found in New Zealand.

Q1: do you think this hull mold was originally used by Boston Whaler to create a Unibond hull?

The essential element of the Boston Whaler boat is the Unibond hull. If you need advice about how Boston Whaler fabricates their Unibond hulls, see these articles:

Original Patent of Boston Whaler Hull Construction
https://continuouswave.com/whaler/refer ... atent.html

Boston Whaler Factory Tour
https://continuouswave.com/whaler/refer ... ctory.html

For general background on Boston Whaler boats, read the entire Frequently Asked Questions answer at

Frequently Asked Questions about Boston Whaler Boats
https://continuouswave.com/whaler/reference/FAQ/

jimh wrote:Q1: do you think this hull mold was originally used by Boston Whaler to create a Unibond hull?

I think someone made a mold off a [Boston Whaler 13-foot hull] here in New Zealand. This mold was made very professionally. It has lasted while stored outside. I’ve since found out it’s looking exactly like a 1968 13-foot Boston Whaler boat.

I found a restored boat with the same hull liner.

https://acbs.org/1968-boston-whaler-partial-referb/

NZwhaler wrote:I found of a restored boat with the same hull liner.

There thousands of old 13-footers, but I do not see any reason the boat in your linked article is particularly able to authenticate the mold you found.

For some individual to use an existing older 13-foot Boston Whaler hull as the plug from which to make a female mold for laminating a similar hull would not be unusual, but you cannot create a Unibond hull from that mold. To make a Unibond hull you need two molds, one for the outer hull and a second for the inner hull or hull liner. Both molds must be reinforced so they do not flex or bend under the considerable pressure created by containing the expanding foam that will completely fill all the space between them.

Further, the liner mold must have a large sprue hole and also distribution vents to allow air to escape. The molds must be oriented at a particularly optimum angle to best encourage the foam to expand into every section of the available space.

And, very important, you must incorporate shear braces to structurally link the hull and liner parts together throughout the two molds.

Finally, you need to join the two sections and introduce the foam while the laminating resin in both halves is still curing.

This is a rather massive undertaking. If you want a 13-foot older Boston Whaler, just buy one and refurbish it. That is a much simpler project.

Another aspect of the Boston Whaler Unibond hull is that the overall strength of the hull is not created just by the laminate lay-up strength. Having the hull and liner completely filled with a relatively high-density closed-cell foam allows for the actual laminate thickness of both hull and liner to be thinner than if they were required to withstand the forces that will act on them in actual use without the foam filled interior.

If you are going to lay-up a hull in your hull mold and expect it to be sufficiently strong to survive for 50-years without being reinforced continuously and completely throughout its structure with a primary-bonded strong connection to the foam filling the interior space, you will need to use a heavier lay-up schedule.

The only other boat that has been constructed in a similar manner to the Boston Whaler is the Everglades boat, designed by former Boston Whaler head of design Bob Dougherty, and constructed using his RAMCAP method. The Everglade boat hulls were also entirely filled with foam, but the process of getting there was different. I will describe the method in short:

The Everglades construction technique was to design the liner and hull molds to have very specific interior spaces when combined. The shape and size of these multiple spaces were computed and measured in advance, and the foam that would fill them was then pre-cast into those multiple shapes. After the hull mold was created, the precast shapes of foam were then bonded to the hull mold with a resin, locking them in place. The liner was then bonded to the hull-foam assembly, producing a similarly reinforced hull.

Bob Dougherty thought that his method would eliminate any possibly of voids in the foam as could be occur during the more or less blind casting of the foam into the hull as used at Boston Whaler.

The Everglades boat method is also complicated, as it requires producing many high-accuracy molds for creating the pre-cast foam inserts.

For more about Bob Dougherty and Everglades Boats, see

Bob Dougherty, Everglades Boats
https://continuouswave.com/forum/viewto ... 986#p21974


The Pioneer in Unsinkable Boat Design
https://www.evergladesboats.com/about-e ... our-story/

Regarding the lay-up schedule used by Boston Whaler compared to what is used in Everglades, if you follow the links I gave regarding Everglades and watch the video showing the actual building of an Everglades boat, there is a mention of the laminate thickness of the hull in a demonstrator model (about 07:08 into the presentation) where the hull sides are not backed with foam. There is a sign attached to the hull that gives the lay-up schedule for that area. Below I have transcribed the lay-up sign:

HULL LAMINATE

1. 25-mills of premium gelcoat
2. 25-mils of vinylester barrier coat
3. 6 oz. of vinylester skin coat
4. 50-mils of polyester print barrier
5. several layers of knitted bi-axial fiberglass

Here is a link to this portion of the presentation:

https://vimeo.com/205815585?fl=pl&fe=cm#t=6m51s

Regarding the hull laminate schedule mentioned above and repeated below:

HULL LAMINATE for a 23-foot hull from EVERGLADES

1. 25-mills of premium gelcoat
2. 25-mils of vinylester barrier coat
3. 6 oz. of vinylester skin coat
4. 50-mils of polyester print barrier
5. several layers of knitted bi-axial fiberglass

The first two layers are specified in a thickness dimension of 25-mils or 0.025-inches

The third layer is specified only by the weight and called a vinylester skin coat. This material is typically applied as a barrier coat to reduce the chance of osmotic blistering in the underlying laminate layers. The specification of "6-oz" does not seem to yield much useful information, as the "skin coat" would be a layer of the special vinylester resin applied to the hull as the hull thickness was being built up. If the 6-oz refers to a cloth, the typical thickness would be about 4-mils or 0.004-inch. Perhaps what is intended to mean is this layer is a 6-ounce fiberglass cloth and the resin used is the vinylester laminating resin.

The forth layer is back to a thickness dimension, a 50-mills or 0.05-inch layer of polyester resin as a print barrier, that is, a layer designed to prevent the weave of the subsequent cloth laminated layers from printing through or being visible from the hull exterior gel coat layer.

The fifth and subsequent additional layers are a knitted cloth of bi-axial weave orientation. Usually the cloth is specified by its weight, but no specification is given.

The biggest difference between the Everglades and the Boston Whaler is that the lay up in a Boston Whaler is gel coat resin followed by sprayed on chopper resin. If there are any cloth layers, they are probably used in certain areas. I do not think the entire hull is ever given a complete cloth layer.