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Author Topic:   drilling and tapping
nolester posted 12-15-2003 08:13 AM ET (US)   Profile for nolester   Send Email to nolester  
I need to learn how to drill and tap into the phenolic [sp??] "whaler board" to mount something on the bow deck of my Sport 130. I've done plenty of drilling, but no tapping. Any suggestions where to learn this? Shoot, I don't even know what it is! Is it just like putting an anchor in, but it being a threaded one?
arnereil posted 12-15-2003 08:38 AM ET (US)     Profile for arnereil  Send Email to arnereil     
Do a search on tap drill sizes to find out what drill size you need to use for the specific bolt. You'll see something like this:

Tapping is kind of an art. Once the hole is drilled, a tap with a tap handle is used to thread the hole .... on metal, you screw the tap in, then reverse the rotation a bit, so it's like 1/2 turn in, then 1/4 turn out, working your way in and reversing to clear out the taped material... main thing is don't rush it. If turning the tap gets difficult, you are in danger of messing up the threads or breaking the tap. With metal, a lubricant is used, with non-metalic material, i'm not sure what should be used.....

kingfish posted 12-15-2003 08:47 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Phenolic is *much* softer than any metal you would normally tap, and the two biggest differences in practice are that you don't have to worry about breaking the tap by turning it too fast, and the pilot hole should be 1 or 2 drill sizes smaller than what you would normally use for any given tap size. Most hardware atores will have charts illustrating the normal drill to tap size relationship.

If you don't already have one, purchase a small drill index so you have some choices in hand, buy the tap and tap tool and do some experimenting on a scrap piece of the phenolic before you go live. I have typically drilled the pilot hole (smaller than for metal) and used self-tapping sheet metal screws (SS) for the work I have done with phenolic, but I don'r know why drilling and tapping wouldn't work.


nolester posted 12-15-2003 09:51 AM ET (US)     Profile for nolester  Send Email to nolester     
I don't know why I wouldn't use self tapping screws, as it sounds easier.

But I sent an email to Boston Whaler and this was response:

"This bracket could be installed on either side. Drill, tap and use machine
screws into the phenolic material."

It is a bracket to hold a stern mount trolling motor off the bow.

Jerry Townsend posted 12-15-2003 10:36 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
nolester - hanging a stern mounted trolling engine with machine screws into whaler board would make me a bit nervous. That is, whaler board is a relatively soft phenolic and the engine is a vibrating load that, as such, will tend to loosen the mounting bolts. And when one bolt loosens, the load in increased to all of the remaining bolts - - and then splash. Consider replacing your plans and use metal instead of the whaler board. ---- Jerry/Idaho
nolester posted 12-15-2003 12:43 PM ET (US)     Profile for nolester  Send Email to nolester     

Here is what I sent Whaler:
"OK if starboard and I use a bracket like this?
[url][url] "

And this is what they said in response:

"This bracket could be installed on either side. Drill, tap and use machine
screws into the phenolic material."

nolester posted 12-15-2003 12:49 PM ET (US)     Profile for nolester  Send Email to nolester     
I'll try that link again:
nolester posted 12-15-2003 12:50 PM ET (US)     Profile for nolester  Send Email to nolester     
And yet again!

Still got a lot to learn!

Tom W Clark posted 12-15-2003 01:06 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

The reason you want to use machine screws in this application is because the motor mount you propose using will put substantial stress on the fasteners holding the mounting plate. Although the catalog page you've linked to does not specify the fastener size, I suspect it will be a 1/4" - 20.

While a #14 sheet metal screw (the equivalent diameter size of 1/4-20 machine screw) might be sufficient, a 1/4-20 machine screw will definitely be stronger so long as its hole is tapped correctly.

Tapping is not difficult. Go to the hardware store and buy the appropriate size tap for a few dollars. I disagree with kingfish's assessment of Whale Board (not whaler board) as being *much* softer than any metal. In fact, Whale Board is only somewhat softer than aluminum which was (and is) also used as backing in Whaler hulls, though mostly in their commercial line of boats.

The most important things to remember when tapping is to use the correct size pilot hole for the tap you are using and then to be careful to align the tap with the hole as you are cutting the threads. Go slowly and reverse direction frequently to avoid loading up the tap with the tailing from the operation.

Tom W Clark posted 12-15-2003 01:33 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Oops, make that Whaleboard, not Whale Board.

Rainier Ritchlite, the manufacturer of Whaleboard, offers some tips on drilling and tapping the material. Milling, drilling and tapping are to be done dry. For more info see:

JBCornwell posted 12-15-2003 02:05 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Ditto what Tom said.

In addition:

Drill the fore-outboard hole through the gunnel and put a nylock nut on it with a flat washer bent to fit the under-gunnel contour.

Use only 5/16" x 18 stainless steel machine screws for the rest.

Learned both lessons the hard way on a 2001 Montauk.

Red sky at night. . .

kingfish posted 12-15-2003 02:36 PM ET (US)     Profile for kingfish  Send Email to kingfish     

Is there a significant difference in physical properties between Whalerboard and King Starboard? Maybe I've gotten my materials mixed up, but I thought the two were almost identical. I've not worked with Whalerboard, but I have worked with starboard, a lot, and it is a *lot* softer than aluminum.

Jerry Townsend posted 12-15-2003 02:44 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
nolester - thanks for the link - quite informative. And, for your information, Tom Clark is very experienced and probably has more experience with whaleboard than many - and certainly including myself.

I will have other comments - but first, you mention that you are going to mount off the bow. Are you using an electric motor or an single cylinder engine? ----- Jerry/Idaho

nolester posted 12-15-2003 03:55 PM ET (US)     Profile for nolester  Send Email to nolester     
Fascinating stuff....

My plan is to mount a stern mount electric trolling motor on the small piece of flat deck in the corner of the bow, using one of the brackets linked-to above. Using the mounting bracket, it will be easy for me to remove it with little or no damage to the boat, and the footprint will be small.

The tapping part sounds fun.

I don't know if there will be any fore-[whatever] and through-the-gunwale stuff. It doesn't look like I'll have anything but some tapped screws into the little deck place I mentioned, to put down the bracket the mount attaches to.

nolester posted 12-15-2003 03:58 PM ET (US)     Profile for nolester  Send Email to nolester     
You didn't do one of these mounts, did you? I figure I'll order the mount and see what the paperworks says about screw size. Maybe I'll call 'em. Then I'll have that fun trip to the hardware store. I'll be a tapper in no time!

ps: just don't want to screw up my boat!

Tom W Clark posted 12-15-2003 04:42 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
John (kingfish),

King Starboard is a polymer plastic and not the same as Whaleboard (not Whalerboard, or Whaler Board, or Whale Board). Yes, it is harder and stronger. I'll send you a sample.

Whaleboard is a laminated paper product made with phenolic resin. It is actually hundreds of layers of recycled content paper product "cooked" under tremendous pressure in a huge press at the Rainier Ritchlite factory in Tacoma, WA. As near as I can tell it is pretty much the same as their Ritchlite countertop material that is now becoming all the rage.


You will want to have the mounting plate in hand before you drill any holes. Once you have it, position the mounting plate exactly where you want it and use a Vix-Bit self centering drill bit to make the initial pilot holes though the fiberglass. This will keep the holes exactly in the center of the holes through the mounting plate and will all but eliminate any errors on your part from having the drill bit "walk" away from your mark.

Vix-Bits are available at most good hardware and home improvement stores. They are VERY useful, and I highly recommend them. There are other brands of self centering drill bits, but I have found the Vix-Bits to be the best. I believe even brokers them.

After drilling through the fiberglass you then use the appropriate size drill bit to create the hole through the Whaleboard that will be tapped. If you do use 1/4-20 flat head stainless steel machine screws you will want to use a #7 tap drill bit (or a 13/64" drill bit) for the pilot hole through the Whaleboard.

To digress a bit, there is often confusion about various popular composite materials used in boats today. Starboard and phenolic board are not the same. Whaler does not use Starboard inside their hulls and they use neither Whaleboard nor Starboard in their transoms.

Whaler does (and always did) use good old plywood to make their transoms strong. They DO use Whaleboard, aluminum and plywood for hardware backing in the hulls.

Jerry Townsend posted 12-15-2003 05:39 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
nolester - your planning on using an electric trolling motor significantly eases my concerns. As such, using the whaleboard phenolic material with 1/4 x 20 bolts as Tom Clark suggests might work. However, being conservative and not taking chances where unneccessary - I would still use a metallic backing plate, given the choice. --- Jerry/Idaho
nolester posted 12-15-2003 05:39 PM ET (US)     Profile for nolester  Send Email to nolester     
Vix-Bits it is! Thanks so much. I will order the bracket and when it comes I will study everything, including this thread, and you'll hear back from me!

I am thinking I better order the motor too, to best judge where to put the bracket.

I'll spare you the electrical questions for now! :)

JBCornwell posted 12-15-2003 06:42 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Hi, Nolester.

No, I haven't used the mount on your link. I got my experience mounting Minn Kota quick disconnect base plates.

Looking at the mount you refer to, though, I see even greater leverage stresses on the mounting screws (bolts) than with the much larger Minn Kota plates.

Red sky at night. . .

jimh posted 12-15-2003 11:22 PM ET (US)     Profile for jimh  Send Email to jimh     
If you have no experience using a tap, and no experience using a tap in phenolic material like WHALEBOARD,, I would strongly recommend a few practice runs with some scrap material. Practice a few holes and taps first, then take a shot at the embedded material in your Boston Whaler boat hull.

Phenolic resin boards are made by several manufacturers, usually graded in terms like G-10, G-9, G-8, etc. The various compositions have different properties of physical strength, dielectric coefficient, and other various attributes.


Jerry Townsend posted 12-16-2003 12:27 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
JB - Your point about the increased leverage is right on - and that was one of my major concerns. However, using an electric trolling motor alleviates that concern - in part because of the lighter weight and also the non-vibratory loading.

In fact, the design nolester was planning on using amplifies the load by a factor of 4 to 5 and places that load principally on the front two bolts. --- Jerry/Idaho

JBCornwell posted 12-16-2003 01:13 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     

Minn Kota motors are electric trolling motors. Did you think I was mounting a gas engine on the bow?

Red sky at night. . .

JoeH posted 12-16-2003 02:51 AM ET (US)     Profile for JoeH  Send Email to JoeH     
I'm not familiar with your sport and where you are mounting your bracket but you will need to know if your holes will be thru holes or "blind". There are different style taps. Get a starter tap to begin with. It has a very gradaul taper and the cutting edges start very slight and work up to the actual thread size. The taper will let you get more of the tap into the hole before you start to cut threads and will help to keep you perpendicular to the work. If you have thru holes, just run the tap down out the bottom of the work until the tap has cut to the full diameter(past the taper) With a blind hole you will need to drill a little deeper than the screw length. Remember to include the thickness of your plate. Start with the starter tap but the taper will not let you cut threads the whole depth of the hole. You will feel it bottom out. Then switch to a "Bottom tap". A bottom tap does not have the lead the starter tap does. The end of it will look almost like a bolt or screw. Thread it into the hole like you would a screw and finish tapping. This will let you cut threads almost to the bottom of your hole, thats what the extra depth is for when drilling. Take your time, back the tap out to clear the threads as mentioned, and above all keep a steady hand and do not side load the tap, they are hard to the point of brittle and not very forgiving. Best of luck, Joe
Jerry Townsend posted 12-16-2003 02:54 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
JB - I had no idea what a Minn Kota quick disconnect base plates was - but your

"... Looking at the mount you refer to, though, I see even greater leverage stresses on the mounting screws (bolts) than with the much larger Minn Kota plates. ..."

is generically true and led me back to the stresses I envisioned in the design that nolester was considering.

And, as I mentioned, using an electric motor is beneficial -being lighter and eliminating the vibratory loading. --- Jerry/Idaho

JBCornwell posted 12-16-2003 04:07 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Sorry about that, Jerry.

I assumed (with the usual risk) that "everyone knows" that my Minn Kotas are front mounted electric trolling motors that mount on about 10" X 12" quick disconnect base plates.

Stresses from running with the motor "up" and when the motor bumps a submerged object are nearly centered on the plate.

My concern with the mount that Nolester is considering is that the stresses will be on the end of an arm that reaches out from the relatively small base plate.

Red sky at night. . .

Jerry Townsend posted 12-16-2003 07:26 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
JB - and as I mentioned earlier - your concerns are right on. The 5 1/2 inch diameter mounting plate means that the bolt circle might be something like 4 3/4 inches - which means that the entire load is going to be amplified by a factor or 4 or 5 and be taken by just two bolts. Your quick disconect mounting plate, being considerably larger alleviates that problem.

And also as you point out - the loads imposed by the trolling motor hitting something must also be considered. These loads can really be significant. --- Jerry/Idaho

nolester posted 12-16-2003 08:26 PM ET (US)     Profile for nolester  Send Email to nolester     
Those 10"X 12" quick release plates are not nearly as asthetically pleasing as the mount I am/was [?] about to use, described by one commentator as an "elegant" solution. Maybe I should get the big, "ugly" permanently defacing, bow mount.

This jack leg is having doubts.

nolester posted 12-17-2003 09:32 AM ET (US)     Profile for nolester  Send Email to nolester     
I am not necessarily affraid to try my hand at this installation. You all have been good teachers here. But I don't want to do it if the underlying idea is a bad one or if it is likely to fail. There is an aire of expertise here, and the suggestions that the stress on the bracket may be overwhelming are causing me to question my best laid plan! Do you guys want to vote on it? :)
Jerry Townsend posted 12-17-2003 12:37 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
nolester - I will not vote - but only offer my comments. In general, the larger the base, the larger the mounting bolt circle - the lower the stress on the mounting bolts and base plate.

I don't know to what loads the mounting systems were designed to - and therefore cannot say any one is adequate or inadequate.

Get the one that appears to be built better of the better material that has the better built and larger mounting system - that will fit on your boat. ----- Jerry/Idaho

andygere posted 12-17-2003 03:43 PM ET (US)     Profile for andygere  Send Email to andygere     
Since most boats are not built like Whalers (inner and outer fiberglass shells with foam bonded in between), I suspect that the mounting plate may have been designed for applications where it could be through bolted with an aluminum or wood backing plate. In general it is an elegant solution, so perhaps a modification of the idea would work for you. You could have a similar bracket fabricated by a good welding shop (ideally one that does a lot of work with aluminum) but with a larger mounting plate to spread the load over a bigger surface area and additional machine screws. A custom mount could be shaped to match the step pad in the bow, and even powdercoated white to make it match the rest of the boat. Perhaps Birdsall Marine would make you one with a mounting plate to your specifications.

Generally speaking, the machine screws will have 2 types of load on them. They will be in varying degrees of tension resisting the load caused the the weight of the motor itself when it's hung on the bracket. Think of the leading edge of the bracket as a hinge; the machine screws tend to be "pried up" with the tubular arm of the mount acting as a lever (or momend arm), which has the effect of amplifying the forces from the weight of the motor. The screws will also be in shear, resisting the horizontal force exerted through the bracket by the motor's thrust (or from striking a submerged object). In all cases, the more bolts used in conjunction with a larger mounting plate will distribute these forces and reduce the load on each fastener (and the material it's threaded into). Also, as the plate gets larger, friction between the deck and the plate takes a larger part of the shear load, and the screws work more in tension literally clamping the plate to the deck instead of pinning it on. Use of a marine adhesive (such as 3M 4200)in addition to machine screws can further reduce the forces acting on the fastenrs.

lakelanier posted 12-18-2003 10:10 AM ET (US)     Profile for lakelanier    
I am considering using this same trolling motor mount and am also concerned that the arm is essentially a lever. My hull is a 96 so it will have wood backing but I do not think screws alone will be sufficient to hold this mount. My previous post ( titled "Method for through bolting using toggle bolts"; I suggested the following:
Drill a hole large enough to accommodate inserting the toggle bolt. Dig out enough of the foam to allow the toggle bolt wings to unfold. Once the toggle is in place (with the bolt still in) inject the hole and cavity created by the expanding toggle with epoxy and let dry. Then remove the bolt. I am planning on wrapping the bolts with Teflon plumbing tape to prevent them from being frozen in the epoxy. Between the toggle bolt and the epoxy plug this should approximate the strength of a through bolted instillation with backer plate.
cape_rover posted 01-09-2004 06:49 AM ET (US)     Profile for cape_rover  Send Email to cape_rover     
Should you apply 'loctite' to the machine screws used to fasten the bracket into the whaler board so the machine screws do not back out? If you should, what type of 'loctite' should you use?

Whalerdan posted 01-09-2004 08:47 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     

Seems to me if you mount a Transom trolling motor to the front of the boat using this bracket, when you tilt the motor up to run you will be tilting the thing out in front of the boat. The motor will be sticking way out in front of the boat adding even more load to the bracket. Also, the handle will be point forward when you operate it. That would probably work, but be kind of weird.

I guess if you just remove the motor everytime you move to a new spot it might work, but what a hassel. If you don't have a motor already, I would buy a bow mount trolling motor. The cost of this bracket and a transom mount motor would be more than a bow mount.

If you do decide to go this way (TM), one thing I was thinking, you could open up the holes on the base of that bracket so you could use larger screws.


lakelanier posted 01-09-2004 01:08 PM ET (US)     Profile for lakelanier    
When using a transom motor in the bow you remove and then reinstall the control handle turned around 180 degrees on the shaft. The motor is then oriented the same way as if it was installed on the transom and the handle is accessible. When not in use it can be raised all the way up and tilted back as well. It will not extend out in front of the bow.
Whalerdan posted 01-09-2004 02:01 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     

Thanks for clearing that up. Can all trolling motors handles be turned around; specifically those white Saltwater Minkota's?

Still though, if you don't have the motor already, it would be more expensive that way. But, it might be more versatile since you could still use the motor on some other boat if you wanted to.


tomroe posted 01-09-2004 09:55 PM ET (US)     Profile for tomroe  Send Email to tomroe     
cape_rover - I wouldn't recommend using Loctite Threadlockers, as they will attack some plastics.

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