CONTINUOUSWAVE

I just bought a 1979 11-footer. I examined the boat thoroughly before I bought it. When starting work on the boat I noticed something odd: in the space [in the bow locker as seen in Figure 1], there seems to be a water drain hole that ends up inside the hull [illustrated below in Figures 2 and 3].







I thought water would come out in the hole [on the foredeck as seen Figure 3], but if a [ long nylon tie-wrap] is inserted into the hole, I feel I can get inside the hull.

I plan to take off the [circular cover plate at the sprue hole as seen in Figure 2] to see what [is] under it.

[Moderator's note: I have identified the three illustrations with figure numbers to allow readers to more easily refer to these illustrations by number, and I have created captions for the illustrations to identify what is being illustrated by them. A long and profusely illustrated reply on a corollary topic has been moved to its own thread.]

marcdd wrote:I plan to take off [the sprue hole cover] to see what [is] under it.

The circular plate seen in Figure 2 is covering a sprue hole. If the circular cover plate is removed the interior of the Boston Whaler Unibond hull will be revealed. At that point the Unibond hull contains foam.

If unfamiliar with the term "sprue hole", a sprue hole is a pouring hole in a mold.

In the fabrication of a Boston Whaler boat with a Unibond hull, there usually is a sprue hole near the bow. During manufacturing, a liquid material is poured into the sprue hole. The hull and liner laminated parts are clamped together to resist the expansion that will occur in te liquid material as it undergoes a rapid chemical reaction and changes into a foam. The clamped assembly is oriented with the bow higher than the stern. The liquid flows to the stern and begins to expand into foam.

The volume of the foam is much larger than the volume of the liquid. The foam expands and fills the mold cavity created by the joining of the hull and liner laminated parts. The sprue hole affords an escape for excess foam as it expands.

After the foam cures into a solid, the foam that was pushed out the sprue hole is cut off flush with the deck level. In some instances a circular plastic cover plate is adhered in place to reduce ingress of water into the sprue hole.

In my experience to see a multitude of rivets fasteners holding a sprue hole cover in place is unusual. However, in this particular instance, the sprue hole cover plate has a small pad-eye fitting attached to it. The purpose of that fitting is to provide a tie point for a rope (or a bungie cord) that will be used to retain in place the bow locker wooden cover. Because of the location of the pad-eye fitting on the sprue hole cover, I suspect that Boston Whaler firmly attached the cover plate with multiple rivets in order to strengthen the fastening of the cover plate sufficiently to resist any pull on it from the rope retaining the bow locker hatch.

If you plan to drill out the rivet heads, do so very carefully and avoid enlarging the holes in the circular plate. There is typically no need to repeatedly remove and reinstall the plate. An adhesive-sealer that is not known for enormous strength might be useful to adhere the circular plate back in position after you have finished your inspection. The use of a sealer would better prevent ingress of water into the foam below the opening. You can also consider using small self-tapping stainless steel screws to re-fasten the cover and to augment its strength to prevent the retaining rope for the hatch cover from pulling loose the sprue hole cover in the future, instead of using rivets.

marcdd wrote:...I feel I can get inside the hull.

I am not clear on your description of what you feel inside the hull. Please clarify

What I would anticipate you should feel is a passage that connections the hole seen in Figure 3 that exits onto the foredeck of the 11-footer to the hole seen in Figure 2 that is at the aft end of the bow locker. This passage is a drain that conducts water from the bow locker to flow onto the deck--or at least that is my inference. If there is not a clear passage between the drain entry hole in the bow locker and the drain exit hole on the deck, the cause of that could be an obstruction. The obstruction could be due to debris that has accumulated in the drain in the 43-years since the boat was manufactured.

I do not believe that Boston Whaler intended the bow locker drain hole to drain into the interior of the Unibond hull and provided no other passage for the water to flow out and onto the cockpit deck.

I would expect [the drain passage between the holes] to be something like a hose or a pipe, or in any case, something that does not enable water to get into the Unibond hull.

I can also put the tie wrap quite far into the boat. When I then pull out the tie wrap, it wet and dirty. I assume that the tie wrap was touching the foam.

My best guess is that the [hose or pipe that I expected to find that connects the] passage between the two holes has fallen off or is broken.

My idea was to open up the sprue hole. Then I will be able see inside the hull and find out what happened. This will also enable the boat to fully dry out.

As a next step, I would then either fix the connection, or, if not possible to fix the connection, just close the holes so no more water can get it.

What do you think?

You can removed the sprue hole cover and let the foam dry out. But I doubt you will see anything other than foam. Or perhaps wet foam.



I don't have any first-hand information about how the connection between the bow locker and the deck was made.

I would anticipate that Boston Whaler might have just made the hole, and Boston Whaler anticipated that water would not sit in that passage but would immediately drain, and left the hose as just that, a hole in the foam and nothing else. Or perhaps the interior walls of the hole were given a coat of resin to help repel water.

If you made the hole diameter larger, perhaps you could then insert a flexible plastic hose into the passage, then cut-off the hose flush at each end, and seal and cement the tube in place.

Remove the sprue hole cover and report what you find.

ASIDE: in Figure 4, the color of the gel coat on your boat has changed to blue from Desert Tan. That is quite odd.

Many thanks. I will let readers know what I find when I remove the sprue cap.

ASIDE: the color change in Figure 4 was just a very early morning picture with bad lighting.

My guess: the hole [that is the topic of this thread in a 1979 11-foot hull] is a factory feature.

The lack of any other drain means that the locker would otherwise fill to the brim .

The depression at the hole in the locker also indicate [the hole was a made at the factory].

If Boston Whaler used a brass tube insert it may have deteriorated long ago.

I would want to retain that passage as a drain, but I would insert something strong and rust proof to act as a conduit. Stainless steel or plastic tubing would work. [Adhere the stainless steel or plastic tubing] to the hull to stop water getting inside the [foam] core.

I did something similar to my 15 footer. I use my bow locker as a fish live well. I have a drain at the bottom that is open to the sea. I leave it plugged until I need the live well. Then I open the drain to the sea.

The well drain sits below the water line and [the well] fills about half way up with sea water when the plug is removed. Under way [the well] drains. At rest [the well] refills.

When the drain was plugged, rain water would fill the locker to the brim. The mahogany locker cover would sit in water until [the water was emptied from the well].

I added a drain very similar to [the bow locker drain on an 11-footer]. I positioned the drain tube to let the locker fill with rain water to within 3-inches of the cover. [Water rising above the rain] overflows onto the deck.

When [the well is] used as a live well, the water does not reach the overflow.

The drain I created is shown in a sketch below. I used a thick nylon plastic tube. I used Marine Tex to seal [the thick nylon tube] to the hull.