Tunnel Questions | Boat Design Net

I have been rebuilding this 27 foot express cruiser fishing boat for a long time.





The boat ended up upside down, banging on the rocks...




I bought it and rebuilt the transom, cab and flybridge. Boat was previously setup for twin Volvo penta stern drives. To "save money" (ignoring the fact that time is money), I got a good deal on a nice used 210HP Cummins 6BT and a ZF-63IV 1.56 v-drive. All I want to do is troll and have GOOD fuel economy at 10 knots. I estimated the completed boat's dry weight to be around 6,200 lbs and a fully loaded MAX weight of 9,200 lbs. We used 10,000 lbs in the prop calculator so I bought a 22x30 3B michigan prop with a 1.75" bore. This is our starting point. I have not bought a shaft yet.

Because of the of the large prop and the requirement to trailer the boat, we decided to go with an 8-inch deep tunnel. Most of the tunnels I have seen have a "propeller region" that is straight. This straight region accommodates the rudder and prop and extends forward of the prop for what usually seems to be about the same distance as the diameter of the prop. So, in designing my tunnel's propeller region, I calculated:

rudder length requirement + prop width + prop diameter = propeller region length

Propeller region:

http://www.fiberglassin.com/wp-cont...de-view-with-pipe-for-shaft-alignment-min.jpg

http://www.fiberglassin.com/wp-content/uploads//12/tunnel-transom-view-min.jpg

http://www.fiberglassin.com/pics/stern-view.jpg

I currently have the last 8 feet of the boat gutted. Put in new inner and outer stringers. Going to install another fuel tank in the center of the boat, a bait tank, and some water tanks that can help with ballast weight and or actually be useful as a fresh water washdown. The boat had "sealed" compartments before that had water in them anyway. I would like the boat to have as much "useable space" as possible even if I don't choose to use it all the time.

I bought a huge roll of brown paper from Home Depot and practiced drawing the curvature for the the front half of the tunnel. I'm not an artist, but after a lot of practice, I was finally able to draw a nice curve that matched the existing hole in the hull and the specifications required for the tunnel entrance. The propeller region of the tunnel is straight and parallel. I calculated the length of the propeller region to be 28 inches long in order to accommodate removing the prop without removing the rudder.

In order to have a 15-degree or less tunnel entrance (as suggested in Blount's paper), the tunnel entrance had to be at least 35 inches long.

After a lot of measuring, I made a paper template that lined up with the existing hole in the hull and allowed me to draw the curve for the front half of the tunnel on the hull. I used the same template for both sides of the tunnel (based off the centerline of the boat) so the tunnel is as perfectly symmetrical as I can get it. After an hour of cutting carefully with the Sawzall, the hole is now complete.

I bought the cheapest Ryobi band saw I could find at Home Depot and cut a template semi circle with a 27-7/8 inch diameter, about 8 inches high. (1/8" accomodates for masonite thickness). I used this template to cut 8 identical pieces out of half inch plywood. I clamped them all together and sanded them as smooth a possible, trying to make all 8 pieces identical. I found the exact centerline of each semi circle (not as easy as it sounds) and marked it with a Bic pen. Four of the semi circles are identical in height. These four pieces are for the propeller region which is symmetrical. I ran the other four pieces across the table saw and removed 1-inch segments from each piece. One is 1 inch shorter, one is 2 inches shorter, one is 3 inches shorter and one is 4 inches shorter. This gives me the slope I need for the tunnel entrance by aligning the semi-circles with the hole I cut in the hull.

I needed a nice solid platform to design the tunnel mold on so that it doesn't change shape throughout the building process. So, I screwed a piece of 3/4in plywood to a couple 4x4's with deck screws. This gives me a nice solid table to build the tunnel mold on. I placed the platform directly under the boat, shimmed to exactly match the same angle that the boat is sitting (using my digital level). Then, I drilled a hole through the centerline of all 8 semicircles using my drill press. I put a 1/2 bolt through all the holes and with nuts and washers, this gave me a way to adjust the spacing of the semicircles so that I can perfectly match them with the hole I cut in the hull. Once I got the semicircles to match the length of the hole I cut, I tightened all the nuts down and the mold got pretty solid.

http://www.fiberglassin.com/pics/-01-26/_.jpg

I tried to align everything as accurate as the thickness of a Bic pen. Not too worried about the shape of the front tip of the tunnel since this will be all glassed in with a shaft log later.

http://fiberglassin.com/pics/-01-26/_.jpg

http://fiberglassin.com/pics/-01-26/_.jpg

My original plan was to build the tunnel insert on a work table 1 inch thick before I glass it into the boat. This was just so that I could "tuck" the tunnel UNDER the transom, rather than just glassing the tunnel to the inside of the transom. I think my plans have changed.

I cut the arc on the transom with a 30in diameter, while the diameter of the tunnel is 28 inches. This gave me a nice 1-inch gap:

http://fiberglassin.com/pics/-01-26/_.jpg

After looking at the 1-inch gap I have around the mold, I think I will be able to lay glass and have it "tuck" under the transom without making a whole tunnel insert on the table and trying to get it to match the hull later on. This will allow me to build the entire tunnel on the inside of the boat and exactly match the inner shape of the hole in the hull. It will give the tunnel an overall better bond to the hull and match the hole I cut much nicer, so I am going to go that route since I will still be able to lock part of the tunnel under the transom. I get the best of everything by building the entire tunnel in the boat. If the boat ever hits the rudder or prop on something, this is going to be a much stronger arrangement than just glassing the tunnel to the inner wall of the transom.

Once I got it all lined up, the spacing correct and the semi circles bolted down tight, I tacked everything down with my trim nailer and pulled the mold out from under the boat and put it on my work table. From there, I used the trim nailer to secure the semicircles to the platform and nail 1-inch strips 1/8* thick masonite around the the semicircles.

http://fiberglassin.com/pics/-01-26/_.jpg

Sanded and faired it all. I have the mold ready to be coated with wax and PVA.

http://www.fiberglassin.com/pics/-02-06/_.jpg

http://fiberglassin.com/pics/-02-03/_.jpg

I still need to finish building some stuff on the inside of the hull. For now, it's nice to get work done via the ability to climb and in and out of the hole.

My main questions are:

What kind of tabbing schedule should I use on the tunnel? How thick should the tunnel be? I will be using 18 oz woven roving and 1.5oz mat. I have about 6 inches from the tunnel hole to the stringers. The stringers are 1.75" microlam LVL.

The original hull looks to be a little less than an inch thick:

http://fiberglassin.com/pics/hull-thickness.jpg

How do you guys radius the actual EDGE of the tunnel entrance (where you cut the hole)? I was thinking of just using an air file or a grinder and doing my best. I don't want there to be a sharp edge right where the new tunnel glass meets the old hull glass.

Anyone have any pics of good working tunnels in this size range?

I’ve got two questions as I’m finishing up scenery on my MR. First, how many of you finish the insides of your tunnels. Not sure if I should finish up the plastering inside or just paint it black and be done with it. Or better said, how many of you show off your tunnel’s inside as part of your layout.

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Question 2: I’m at the point of finishing up my operating drive-in theatre. Need suggestions on gravel to use for the parking lot. Wasn’t sure if I should use ballast or some other type of “gravel” for this. Need kind of a bleached out color. I know ballast does come in various colors just wasn’t sure if this would be too course for the lot. Many thanks!

I put full scenery in my subway tunnels, but the whole idea was to create the right environment for the video camera in the first car of the subway train.

http://www.youtube.com/watch.php?v=dOV9NSqrQlc

I personally enjoy the video camera effect, and as I put more above-ground scenery in, I bring the subway up every now and then and watch the show on TV. It’s a big hit with the spectators, too, particularly the kids.

For my subway walls, I used strips of styrene. I took a hint from the textured ceiling, and applied Hydrocal with a paint roller, let it dry and painted it with light gray primer. My tunnels are lighted inside. The video was taken a long time ago, and since then I’ve added a couple of bright LEDs to the front of the train to improve the lighting.

I recall visiting a club that had two very visible tunnel interiors, protected with plexiglas. The double track main paralleled the aisle on two different levels. One had been finished with a rough, ‘blasted through the granite’ appearance. The other was finished with a concrete lining, including safety bays. Both were a couple of yards long, the effect was impressive and only the club members knew that the tracks were on opposite ends of a lengthy main line.

My ‘maybe in the future’ plan book includes a similar underground diorama of a brand-new bore being cut by an operating TBM. It’ll probably get built shortly after I dock the Emma Maersk at my intermodal port.

Chuck (modeling Central Japan - 200 KM from the nearest salt water - in September, )

Can we assume that this is H0?

1. How much you put into your tunnel(s) depends a lot on where they are and what can be seen from all normal viewing positions.

Humour can be fun… BUT you do not want people leaning over to look into the tunnel! They will catch things with their clothes and limbs. [:O]

You may want to think more about how you are going to do maintenance in a tunnel than how you will scenic it…

You do not want to make a tunnel a dust trap, somewhere nice for bugs/vermin to live or somewhere you have to use an endoscope to do any work in… including just getting out a last car that got uncoupled…

Where your tunnel is somehow close to a viewing face of the layout (like if you have a hidden curve in the tunnel) it cn be fun to be able to look in and see the train in the tunnel through like a horizontal mine shaft. (Cut in from the front of the board… as distinct from looking in the tunnel mouth) If you do that it gets to be worth detailing the tunnel wall that you will be able to see. You will also quite likely want to arrange some illumination… LOW temperature!

About the most important thing is to be able to keep up the maintenance on this part of the layout.

Ballast/gravel road surface.

If you can go get some road surface material and a piece of ballast. Hold both in your hand and compare all three… then look at the size of the hand on one of the figures on your layout.

Ballast does get degraded and get dirt in it… BUT it starts out passing through a 2" ring in the screening process and isn’t much smaller. You would not want to walk around a drive in theatre if it were lossely paved with (old) ballast. (Okay, it

This is HO scale, forgot to mention that. I purchased some fine grade ballast in light gray yesterday and it seems to look pretty good. I do sift my groundcover a second time with a fine strainer and you’d be surprised on how much doesn’t make it through the screen. I went ahead and built up the parking lot humps and just need to cover the lot but not before adding the speaker poles that hopefully I can get to light up.

The two side by side tunnels I have are curved and about two feet long. The top is made to pop off for maintenance and uprighting derailed cars. I thought about putting in a hobo camp or something halarious in the tunnel. The hard part is being able to blend in the pop offs so you can’t see any creases or gaps between the top and tunnel itself. So I went ahead and placed the top on an oversized piece of very thin styrene and blended in the scenery. Essentially the tops just sit without any adhesion to the tunnel itself. Thanks for all the great help! [8D]

Steve,

An interesting read, especially the tunnel comments as I am builing mine now.

Whew, I built the mountains, really liked them, used some paper rock homemade portals and stopped cold. Why? I realized I need to ‘line my tunnels’. OK, so I built some ‘paper and cardboard’ liners. I fitted them in from the back. Yuk, the paper portals looked awful. ANd the lines were only a bit better.

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So I purchased some plaster portals and fitted them to my paper liners. Even more yuk! So I built some styrene liners and started installing them and the plaster portals. Ready to glue it down and stopped cold again. I needed to paint the styrene tunnels which turned out to be no trivial task as the acrylic paint bubbles on dirty plastic. (First time I tried to paint any styrene with acrylic paints you know). OK, painted lets glue. Oh no! The track needs to be balasted but the roadbed needs to be painted first.

At that point, I was glad my mountains were light and removable, so off they came, and I started ground up.

1. widen roadbed so tunnel liners have no gaps. I use 3/4 masonite strips glued to the sub road bed edges like they do in spline roadbeds to fix narrow places on the roadbed.

2. Paint roadbed very dark grey

3. Align track one more time and replace missing ties.

4. Ballast track all the way past the liner and outside the portals

5. Check liner paint job

6. Trimed liners to fit with retaining walls

7. Paint and weather the portals and retaining walls. What a kick that was!

8. Glue liner to portals

9. Glue portals to roadbed

10. Installed retaining walls

11. Reinstalled mountains

12. Plaster cloth repairs to mountain shells

13. Now ready to so some scenicing.

Never did I realize it was so involved in making mountains and portals and such. But boy do I like the results.

I’ll post some pictures later, gotta run!

I am not unduly fond of tunnels but I have had a few of them on my (N-Scale) layouts over the years. None have ever been long enough to swallow up more than a dozen or so cars of a train.

If the tunnel in question is straight I usually put a flat black tinted lining stretching 5" to 6" in from the portal. I always leave the middle of the tunnel open, at least on one side to facilitate operation of my 0-5-0 switcher. I don’t use as long a tinted lining with a curved tunnel as with a straight one.

I heartily recommend leaving 0-5-0 switcher access into your tunnel. Bill McClanahan of Texas and Rio Grande Western fame once did a cartoon to accompany one of his magazine articles which showed a character with a fishing pole jabbed into the mouth of a tunnel while he tried to retrieve a derailed car with a fishhook. Believe me, you have never known the height of frustration until . . . . . . . . . .

If you don’t use ballast for gravel what are you going to use???

I haven’t been to a “passion pit” since and I’m not sure I ever went to one with a gravel parking area; I will presume, however t

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