posted 01-14-2007 10:36 AM ET (US)            

[Getting back on topic, the following comments about adding trim tabs to a classic Boston Whaler boat were provided--jimh.] Accurately mark the locations for the tabs and their mounting holes by using two-way tape to attach the hinges to the hull. whether to drill and tap, or use the screws that come with the tabs, the use of two-way tape to temprarily place the tabs prior to drilling to ensure everything will The tape is strong enough to temprarily install the tabs too, to make sure everything will clear them (and they will clear everything) during operation. Remove the hinges from the boat with a wooden wedge when all holes have been drilled.

Drill and tap holes for Stainless Steel Machine screws, instead of using the screws provided with the tabs. The wood-type screws are provided, in part, because professional installers don't want to spend the extra time and effort it takes to drill and tap.

Make a plywood template to set the initial adjustment of your tabs per manufacturer's specifications. My tabs were to be set at 7 degrees, so I made a plywood template that fit under the tabs and extended about ten inches under the hull. This allowed me to initially set my tabs at exactly seven degrees.

posted 01-14-2007 01:16 PM ET (US)            

Accurately mark the locations for the tabs and their mounting hole by using two-way tape to attach the hinges to the hull. Whether to drill and tap, or to use the screws that come with the tabs, the use of two-way tape to temprarily place the tabs prior to drilling will ensure everything lines up properly. The tape is strong enough to temporarily install the tabs too, to make sure everything will clear them (and they will clear everything) during operation. Remove the hinges from the boat with a wooden wedge when all holes have been drilled, but prior to tapping.

posted 01-14-2007 02:27 PM ET (US)            

Makers of trim tabs usually have customer support lines and people can call them if they have specific questions about the installation instructions for those products. I am sure they get a lot of calls. I did review the manufacturer's installation instructions for several brands. I thought they were sufficient to explain the process of installing the tabs. However, as I mention, the manufacturers' instructions do not take into consideration the transom configuration as seen on a classic Boston Whaler. That is the fundamental reason for my article. I think I explained it in the first sentence; I will repeat it here.

"Because of the construction of the transom of classic Boston Whaler hulls from 18 to 27 feet, special consideration must be given to the location for mounting trim tabs."

posted 01-14-2007 11:13 PM ET (US)            

There are three photos which may be informative/helpful to your readers who have twin engines, and that detail further some of your points in the article.

The first details the trim tab install, mounted outboard of the raised portion of the transom, and includes detail of how the tie-down points were relocated on the trailer to accommodate the trim tabs.

[Dave's photographs and comments were moved to the article itself--jimh.]

Again -great article...It would have been helpful in my installation, so I hope it helps others who are considering this modification.

posted 01-28-2007 01:17 PM ET (US)            

I do not have any information which would cause me to believe that it is necessary to use a machine screw and tap and thread the hull laminate. One problem I do see with using a machine screw and drilling and tapping the laminate is the potential for the depth of the hole to be improper. With a self-tapping fastener the pointed nature of the fastener and its self-tapping design insures that the hole it makes is no deeper than needed. If one undertakes the process of drilling and tapping holes for all of the fasteners on a trim tab, you may make the holes too deep or not deep enough. Neither outcome is attractive.

If the holes are not made deep enough, the blunt bottom of the machine screw will be forced into the hull laminate when it is tightened, which may cause a crack. Or, even worse, the fastener could be tightened until it bottomed out, leaving some play in the mount. If the hole is made too deep, there will be a void at the bottom. In general it is best to avoid creating any sort of void in the hull, particularly in an area which will be submerged most of the time the boat is underway. While you could fill the hole with excess sealant, my feeling is that the least amount of material removed from the hull structure the better. Undisturbed laminate adds more strength than a pocket of sealant at the bottom of a hole.

Also, I have not seen any information which shows that a constant diameter machine screw produces a higher strength fastener in a material such as the resin and cloth laminate used in a Boston Whaler boat. In places where Boston Whaler does use machine screws for fasteners, they embed a material such as WHALEBOARD or ALUMINUM for holding the threads of the machine screw. They generally use self-tapping screws in areas where the fastener is being held in just the laminate of the hull. Thus Roy's recommendation is contrary to the practices of Boston Whaler.

Also, the threads of machine screws are generally rather fine and closely spaced and may not provide even as much strength as that of a self-tapping screws, those threads are generally coarser and more widely spaced.

I would be glad to include any first-hand reports of where a self-tapping screw failed due to the lack of strength of the fastener's purchase into the laminate material of a Boston Whaler hull when holding a trim tab.

I also observe that the forces on the hinge attachment are mainly shear forces or compression. The length of the fastener may be of more importance than the design of its threads, in that case.

As for Roy's advice on how to mark the holes, I agree. I think it resolves to a form of general advice, which is: mark any hole carefully before drilling into the beautiful hull laminate structure of your Boston Whaler boat. For those who were not aware of that principle, I regret that I did not explicitly provide that advice in my article, but I suggest that it more or less goes without saying. When installing anything on your Boston Whaler boat it is a darn good idea to carefully mark and check the holes before drilling them. If you need to hold a work piece in place as a template, use of a temporary adhesive like tape is certainly one solution.

Roy's advice to make a jig to hold the tab in a preset location when the actuator has been fully retracted in order to determine the location of the actuator base mounting holes echoes similar advice provided (in at least one case) by the manufacturer in the detailed instructions they include with their products. I certainly have no quarrel with that. As I noted, the purpose of my article is not to give specific instructions on how to accomplish the installation of trim tabs--I leave that to the manufacturer--but rather to demonstrate several variations in location on the unusual transom of a Boston Whaler boat.

posted 01-30-2007 12:50 PM ET (US)            

My engineering rationale for recommending drilled and tapped fasteners was due to the nature of the materials being joined. In this case, a metal plate to a fiberglass plate, and to the stresses involved: mostly shear with some tension. In both cases, the thread form is of little consequence, since the root area of the fastener is where all of the strength is. In other words, the point of failure will be what's left of the shank once the threads are cut into it.

There is much more here mechanically speaking, but generally, the number of engaged threads needed to effect full strength is relatively few. Usually around three to five threads will yield a strength (in torsion) that will exceed the strength of the root area of the fastener. In shear, you theoretically don't need any. Don't try this at home, however.

In the case of joining two thin members, i.e. the metal hinge plate of the trim tab and the fiberglass hull, there will likely be plenty of thickness to affect a joint equal to its task. However, where the widely spaced threads of the wood style screws supplied are concerned, there may or may not be enough threads engaged to achieve full strength. With fine (or even course) machine threads, there is a greater likelihood of achieving full fastener strength.

Add into this, the risk of chipping away some of the fiberglass thickness due to trying to force the large thread diameter of a wood screw into the undersized hole and we may loose some of the precious thickness needed to approach full strength.

My point here is that while full strength is not actually required for this joint, one has a better chance of achieving it with machine screws.

Regardless of whether the drilled hole is ultimately for a wood screw or a machine screw, it needs to be drilled to an appropriate depth. Normally, this is going to be "through" the fiberglass of the hull and into the foam behind it. When this is the case, the hole depth is much less critical in either application, since either a pointed wood screw or a blunt machine screw will both readily compress the foam. If the pilot hole is not drilled deeply enough, either screw is going to bottom out, and no "self tapping" feature is going to improve the outcome.

Having said all of this, it's not likely one could go wrong by following the manufacturers recommendations. I do, however, stand by my analysis of the joint, and the notion that the screws used by the manufacturers and/or installers are chosen for a variety of reasons not related to performance, such as cost of the components and the time required to do the job.

As Paul Harvey would say, "Now you know.....the rest of the story"

posted 02-14-2011 09:33 AM ET (US)            

After seeing a report on Ship Shape TV about the Nauticus Smart Tab, I read many comments about owners who had installed it. All comments were favorable. I ordered a set. The ones for my boat are 9" wide by 7.5" deep, SS with 60 lb. rubber booted gas shock absorbers. They are installed as far outboard as possible, flush with the hull bottom, and at a nominal 25 degree angle to the bottom. Although they follow the lateral angle of the hull, this does not matter in performance.

These are not controllable. They work on their own absorbing transom "shock" in all modes of operation. Coming out of the hole the bow rises very little. I can even come out of the hole with two people seated full aft! Likewise, the min. speed on plane is reduced almost 5 mph. They provide both longitudinal and lateral stability and allow me to trim the engine up two or more increments giving almost 100% longitudinal thrust and 3 mph higher top end. Unlike powered tabs, these are continually working to stabilize the hull. At about 22 mph, the tabs are forced full up by water pressure giving NO drag at all. Again, since they are installed farthest outboard, they give max. lateral stability.

As far as mounting hardware, I used the SS screws provided, but after marking and drilling holes, I use a countersink bit to slightly chamfer the gel coat opening allowing more room for the 3M 5200 sealant to form a hole gasket.