PS Advisor: July 2001


Lexan vs. Plexi
Im planning to replace my wooden companionway boards with translucent plastic. Is there a difference between Lexan and plexiglass? Can both be sawn, drilled, and sanded? Which would be better for this application?

-Klaus Schaefer
Mississauga, Ontario

Lexan is a trade name for a polycarbonate that’s made to specific standards. The term plexiglass these days covers a lot of clear plastics with different properties and a range of uses. Both Lexan and plexiglass can be sawn, drilled, and edge-sanded, but both will melt if too much friction is applied too fast, so be careful and go lightly and slowly with saw and drill. Also, the areas where theyre overheated become brittle and will almost certainly crack if you set a screw too hard or have to saw through the area. Lexan will likely be a better choice for your companionway slats. Practice with a spare piece before you commit to your finish pieces.


Air For Your Diesel
With todays compact, well-insulated engine compartments, sustained motoring generates a high-temperature environment for a marine diesel. Would it be worth the effort in terms of improved engine performance, to provide fresh (cooler) air ducting to the engine air intake as you find on many automobile engines ?

-Keith Baldwin
Avon, CT

Absolutely. It takes a very high temperature in the engine compartment to have a noticeable effect on an engine’s immediate performance, but by that time you’re doing your engine no good. If you want to increase a diesel’s general well-being, extend its life-expectancy, and improve its performance over the long haul, give it perfect fuel, change its oil, wipe it clean often, and usher a good flow of cooling air to the engine compartment. Diesels need to breathe.


1. We have a Nexus Fluxgate compass and want to know if it can be mounted near an aluminum mast.

2. What do you recommend for Sound insulation for an engine box, and how do we discover how it is to be installed.

-Tom and Sharon Oler
Metairie, LA

By itself, an aluminum mast shouldnt have any effect on a fluxgate compass (we’re talking about the transducer/sensor part here). The trouble is, aluminum masts often have masses of wire in them and other bits of ferrous metal and fasteners nearby. When you hold the fluxgate in position near where you want to put it, turn on the system, then turn on all the lights on the mast and see if they have an effect. You can also use a regular handheld compass to check for sources of deviation in the area where you want to mount the sensor. Depending on where your light, radio, and instrument cables exit the mast, you might be able to locate the transducer a couple of feet lower.

Fluxgates are sensitive to poor positioning-its best to mount them as low as you can, and near the center of the boat to minimize the effects of roll and pitch. If you find a lot of interference from keelbolts or other chunks of metal, try it in a couple of other places in the boat. Some people recommend mounting sensors aft of amidships, and outboard, like in a cockpit locker.

To answer your second question, standard engine box insulation is a sandwich of open-cell foam on both sides of a PVC plastic sheet. The sandwich has a shiny foil face on one side and adhesive backing on the other. It comes in different thicknesses. You should install the thickest that will allow good clearance all around the engine inside the box. (When you have to choose between too much noise in the cabin and not enough circulation in the engine box, put up with the noise and give the engine air. See Q&A above.) The foam is available from West Marine and other marine stores. The adhesive is prone to failure, so some professionals epoxy or tap studs into the engine box surfaces so that the tips protrude when the insulation is pushed over them. The stud tips are then fitted with washers and nuts, which hold the insulation on better.


Lingering Fuel Smell
We recently bought a 25-year-old trailerable sailboat with a 25-year-old water tank. Given the age of the tank, we decided that we would purchase the boat and bring along a portable water tank for drinking water.

On emptying the tank via pumping the sink faucet, we determined that someone in the boats past had mistakenly placed diesel fuel in the water tank…not much, but enough to add some zest to the contents and to create an unmistakable petroleum-based odor emanating from the tank.

We still don’t plan to use the tank, but the question arises… Is there some way to clean the tank or at least mask the petroleum odor coming from it?

-Jim Smuts
Richmond, VA

We’re going to assume that the tank is plastic or fiberglass, and that there was at least some water in it when fuel was pumped into it. We’re also going to assume that you probably won’t get all the odor out. But here’s the way we’d try to make a dent in it:

Chances are that a lot of the odor is coming from the soft hose to the galley pump, which might have absorbed some fuel early on. If you change the hose, you’ll probably get rid of some of the odor right there. But do that after trying the following:

Put a couple of teaspoons of liquid dishwashing detergent into the fill pipe, then fill the tank with very hot water. Let it slosh around for a couple of days. This should cut through some of the oil residue. Rinse the tank thoroughly, then put in a cup of bleach, refill the tank, and let things slosh around for another couple of days. (Bleach is mostly good for dealing with bacteria in tanks, but it might help here as well.) Then flush the tank thoroughly again.

With luck, you’ll get the tank to the point where you can use it for non-potable purposes like initial dishwashing, handwashing, boat-rinsing, etc. But you also might want to have a look to see how hard it would be simply to remove the offender and replace it with a tank less reminiscent of a truck stop-or use the space for stowage. There isn’t enough room in a trailerable sailboat for a large space not doing its part.

Practical Sailor has been independently testing and reporting on marine products for serious sailors for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising or any form of compensation from manufacturers whose products we test. Testing is carried out by a team of experts from a wide range of fields including marine electronics, marine safety, marine surveying, sailboat rigging, sailmaking, engineering, ocean sailing, sailboat racing, and sailboat construction and design. This diversity of expertise allows us to carry out in-depth, objective evaluation of virtually every product available to serious sailors. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser with more than three decades of experience as a marine writer, photographer, boat captain, and product tester. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.


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