CONTINUOUSWAVE

I don't know what you call the things that the bolts that hold on the brackets of the side rails screw into. Whatever they are called, I need to know the length of the bolts that screw into them. It looks like [the length of something] is 3/16-inch.

bobross wrote:I don't know what you call the things that the bolts that hold on the brackets of the side rails screw into.

Perhaps you are trying to refer to the rail mounting base.

bobross wrote:...I need to know the length of the bolts...

By "bolts" I think you mean a machine screw fastener.

Generally a railing on a Boston Whaler boat ends at a rail base. Does the object you are inquiring about look like the object seen below:


Fig. 1. A railing terminating onto a rail base.

bobross wrote:Whatever they are called, I need to know the length of the bolts that screw into them. It looks like [the length of the fasteners would be] 3/16-inch.

Do you have any existing fasteners from the original installation? Typically a machine screw with a slight taper and a thread-cutting leading edge was used by Boston Whaler to fasten into a rail base. Typically if the tube is retained to the rail base, there will be a hole in the tube through which the fastener passes without being threaded to the tube. The rail base has a post, and the screw fastener threads into the post of the rail base.

A machine screw length of 3/16-inch sounds rather short. A close visual inspection should reveal the existence of existing threads already cut into the rail base by a previous screw. This should allow you to choose the proper machine screw size and length to use for a replacement machine screw fastener.

On my 1966 13-foot Boston Whaler Sport, the side rails went through what I call standoffs or stanchions, and the end of the tubing was drilled and secured with a horizontal screw into the hull. The standoffs were attached through the hull to backing plates with oval head machine screws, as pictured below.

Tom has it. His picture is what I have, less the machine screws.

How long are the screws?

The screws appear to be 3/16-inch diameter, based on trying other screws from my stash that fit into the backing plates.

The item pictured in Figure 2 is a railing stanchion support bracket.

Machine screws are not specified by their thread diameter in inches. The thread diameter is described by a gauge number, usually 2, 3, 4, 5, 6, 8, 10, or 12.

TOM--thanks for the very clear illustration (in Figure 2) of the method used by Boston Whaler to fasten the stanchion support bracket to the hull. I did not realize that the base of the support was through-bolted through the hull sides.

I think the through-bolted side rails were in the earlier years, My 1981 does not go through the hull and nor was my 1978.

bobross wrote:How long are the screws?

In illustration Figure 2 (above) there is a ruler in view that is oriented parallel with the machine screws. I would expect that by careful observation of Figure 2 one could make a darn good estimate of the length of the machine screws shown in that illustration.

Biggie - We have the through-the-hull fittings on our 1981 Sport 13. Perhaps it was a mid season change?

As to the screw length [shown in Figure 2], [the length] could be 1.5-inches (shown) or more, depending on how far the screws are turned into the backing plates.

[How far into the backing plates are the screws in Figure 2 threaded?]

bobross wrote:[How far into the backing plates are the screws in Figure 2 threaded?]

Since you have a 1977 SPORT 13, and I presume your interest in the length of the screws means your boat uses the same method of fastening the stanchion support to the hull sides, I recommend you measure the thickness of the hull of your boat at the location the backing plate will be installed, and then deduce the length of the screws.

Also, machine screws longer than 1-inch are generally not commonly available in small increments of length, so you may need to buy a machine screw that is slightly longer and cut it to length.

Also, a machine screw of 1.5-inch length will cost less than $1. I recommend you buy one and try it to discover if it works. Hardware like machine screws can usually be returned and a credit received, should purchase of a longer machine screw be needed.

I had the wrap around railings on my 13's and 15's, maybe they do not use the through hull fittings. Do you have just the standard side rails? If so that would explain the difference.

Biggie - Yes, side rails only. That would explain the difference. Wrap around railings spread the stress more widely and require less support, or not?

My 1968 13-footer has [railing stanchion support brackets] with the through-bolt and backing plate arrangement shown in [Figure 2]. Mine are in the same condition.

[Note the purpose of giving illustrations a number is to permit them to be easily referenced in text that wants to refer to them—jimh]