Modifiing a Phil Thomas Stealth (Vs. #1) to be NAMBA legal

[longballlumber]

NOTE: Anyone reading this should know that Phil has updated his molds and his current PT Stealth 30 (Version #2) meets the currently NAMBA rules. My hull was purchased before he updated the molds to meet the rules.


Hey group,

I haven't post much lately with pictures so I thought I would document the modifications to my Phil Thomas Stealth 30 to meet the NAMBA transom rules that I started today. If you recall; there was some discussion about a year ago about the boat not meeting the 65% transom rule. The actual rule can be found in the NAMBA as stated below.

Section 28: Page #9 vii) The width of the transom bottom shall be no less than 65% of the
width between the inside edges of the front sponson planning surfaces.
An exception to this will apply to scratch build scale designs of full
sized boats that are full bodied 3 points hydroplanes but have an
afterplane that tapers sharply at the transom. Example: Lauterbach
shovelnoses.

Here are some pictures of the hull with measurements before I started doing work. As you can see the measurement of the “inside edges of the front sponson planning surfaces” is (roughly) 11.125”. 65% of 11.125 = 7.25 (7.23125). You can see in the pictures the transom at its point nearest to the water line is around 6.75. This means I will need to add .75 (total) .375 on each side to meet the measurement. An interesting note to point out is; my hull (version #1) there are two little air traps that Phil put in to the transom to help “pack” some air and lift the transom. Those “nubs” are roughly .125” on each side taking up .25” of the total width. I would like to note the actual transom width is 8” meeting the rules. It’s the non-trip width that everyone seems to be reading. Take a look at the pictures below.

Another thought that I had today while reading the rule before hacking up my boat; is they don’t tell you in the rule book where to measure your transom (i.e. upper or lower). I was corrected below by Fluid on my reading of the rules....

[longballlumber]

Here are a few more before shots...

[longballlumber]

In addition to fixing the transom issue I will be making some CG changes by moving the motor/motor mount further forward. So the first thing I did was unbolt everything off of the hull. At this point the only thing I can do is start sanding. I sanded off the “nubs” that help define the transom air trap. By sanding off the air trap “nubs” I have already increased the transom width (nearest the water surface) by .125 on each side (.25 total) without adding any material. That will still leave me another .125 on each side (.25 total) to meet my target of 7.25 total transom width.

[Fluid]

...they don’t tell you in the rule book where to measure your transom (i.e. upper or lower)....

I guess I'm confused, the rules state this:

The width of the transom bottom shall be no less than 65%...

The issue has always been with the transom bottom, not the total transom width.


.

[longballlumber]

One thing I have been trying to explain to boaters via OSE posts without providing the pictures is nesting your stuffing tube. You can see in the pictures that I have actually glued/glassed in the next size bigger brass tube into the hull (9/32” I think). This will allow me to slip through the proper sized ¼” stuffing tube for Teflon tubing and the use of .150” cable. This is important to point out because the ¼” tube was easily removed so I could work on and around the hull without need to tear out or cut out the glued in stuffing tube. When my work is done, I will simply work in another stuffing tube NO GLUING NECESSARY! Below are some picures before removing the 1/4" stuffing tube. Notice that I have some black shrink at the seam inside of the hull to help seal the two tubes...

[longballlumber]

I guess I'm confused, the rules state this:


The issue has always been with the transom bottom, not the total transom width.


.

Yep, you got me.... I missed that one... I should have re-read it closer. It's been awhile since we had this discussion. It was an honest mistake.

Now that we are on the subject, does the non-trip really make a difference? Assuming your overall transom width (NOT measures from the narrowest point of your NON-TRIP), is legal. In this case that would be 8”. Changing the angle of the non-trip is what will change the overall “width” of the transom. One extreme and you end up with a hull bottom that is an extremely shallow “V”. Go the other extreme and you end up with no non-trip at all and just transom sides that are perpendicular to the hull bottom… They should only be defining what a ride pad/surface is (depth and width) and only measuring the overall transom width (inside of any “ride pad/surface” as defined in the rules…

Now that your not confused by my wording any longer tell us, what's your take on the rule, how it reads, and the intent...

[longballlumber]

In order to keep things as light as possible on the transom I am going to use balsa wood and fiberglass cloth to add the material needed. The balsa will be adding the material needed and I will use the fiberglass later to strengthen/skin the balsa. You can see I have cut a couple pieces slightly oversized and glued them to the face of the non-tip surface.

For the gluing process, I used my West Systems 205/105. I wanted to quickly show how I am measuring out small batches of West Systems to minimize waste. Anyone who has used West Systems 105 system knows that it’s a 5:1 ratio of resin to hardener. I use disposable syringes I measure and mark in 1/8” increments. So the first line on the resin syringe is 10/8’s (or 1¼”). On the hardener syringe I make a mark at 2/8’s (1/4”). This will make a nice small batch for gluing.

[longballlumber]

The following show’s my current status on the project. I hope to do more work today.

You can also see an extra set of lines on the syringes. This is in case I need a “double” sized batch…

Later,
Mike

[Fluid]

Now that we are on the subject, does the non-trip really make a difference?

One of our club members designs and builds his own hydros, and he found that one of them did not meet the transom width rules. He added a filler to remove the non-trips and widen the transom bottom, and he was not at all happy with the way the boat cornered. We run in choppy water much of the time, on smooth water the difference may be less. I know that virtually all successful full scale hydros have non-trips. A few designs in the past did not, but they were either not successful or were not copied.

Now that your not confused by my wording any longer tell us, what's your take on the rule, how it reads, and the intent...

My interpretation means nothing of course. The intent is to eliminate "riggers" like those which have shown up as most of the current successful gas sport hydros. This has been a real bone of contention among gas boaters. But really, Sport Hydro is not Scale Hydro, and if someone only wants to race with boats that look like the "real thing" then he needs to build a scale boat, not a sport boat. IMO.




/
.

[longballlumber]

One of our club members designs and builds his own hydros, and he found that one of them did not meet the transom width rules. He added a filler to remove the non-trips and widen the transom bottom, and he was not at all happy with the way the boat cornered. We run in choppy water much of the time, on smooth water the difference may be less. I know that virtually all successful full scale hydros have non-trips. A few designs in the past did not, but they were either not successful or were not copied.

My interpretation means nothing of course. The intent is to eliminate "riggers" like those which have shown up as most of the current successful gas sport hydros. This has been a real bone of contention among gas boaters. But really, Sport Hydro is not Scale Hydro, and if someone only wants to race with boats that look like the "real thing" then he needs to build a scale boat, not a sport boat. IMO.

/
.

UGH... This is the huge reason why I don't post much on these forums... sometimes typing out a response can lose its meaning so easily or it doesn't get conveyed the way I want...

I didn’t necessarily mean to remove the non-trip… My comment was based on the idea the non-tip angle verses the overall transom width. Anyhow… Here is a picture to show why I would prefer to see them allow the measurement of the overall transom specifically to this hull. The non-trips on this hull that are causing the issue don’t fit the intent of the rule. This boat isn’t an “outrigger”

The lower pictures show how the non-trip angle can grossly effect the transom measurement BUT not change the overall transom width or provide a distinct performance advantage.

My major purpose of this series of post was to so my repair methods of a particular modification so hopefully it can be a learning experience for others. The fact that it’s the PT hull and it didn’t fit the NAMBA rules is secondary. I didn’t need to change the boat as our club (as well as many others) didn’t have a problem with the current hull configuration of the non-trip/transom width.

I will post more as I progress.

[ray schrauwen]

Sorry to spam but, every time I here about this rule my eyes roll. IMPBA says it's o.k. NAMBA doesn't.

[Shooter]

Woah! Mike! I can't believe you are messing with that boat! That thing ran beautifully!!!! Looks like you are doing a great job as usual though.

Just out of curiousity....how far up are you moving the motor? ....and where does your stuffing tube exit the bottom of the hull?

Thanks,
Pete

[longballlumber]

Thanks Pete,

Your right it did run well, but I feel it could be better. Everyone is always raising the bar for this class. I gotta stay on top of things. I've done more work and need to update the thread. I will get some measurements for you over the weekend.

Later,
Mike

[phil t]

Work looks good, really dont have to add much material.
Here is a picture of the new bottom Just wider and with out the small airtraps.
DSC02265 (800x600).jpgDSC02267 (800x600).jpg

[longballlumber]

Alright fellas,

OK back on topic… I’ve gotten more work done over the last few weekends. I will get you caught up where I am as of this morning.

After getting the added material glued to the boat I went ahead and sanded the balsa down to match the hull surfaces and adds the necessary width to the transom. You can see in the pictures I had some gaps to fill. I also used masking tape to create a dam to hold the epoxy filer where I want it; in this case to help make a sharper (less rounded corner).