Mid Size Power Boats

Mid Size Power Boats

A Guide for Discriminating Buyers

by David Pascoe

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Chapter 11

Electrical & Plumbing Systems

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Table of Contents

Flexibility is in the Switching
AC Power - How Much is Enough?
Shore Power Cables
Shore Power Connectors
Electric Service Panels
Circuit Breakers
Service Outlets


Gas or Diesel?
Water Where It Shouldn't
Inverters: AC Power From Batteries
DC Systems
Battery Chargers
Older Boats

Plumbing Systems

Sea Cocks
Plastic Valves
Sea Strainers
Plastic Components
Plastic Nipples
Vacuum Head Systems
Boating in a Sewer
Standard Electric Pump Systems
Waste Plumbing Systems
Bilge Pumps
Where Does the Water Go?
Fresh Water Systems
Dockside Water Systems
Air Conditioning Systems
Assessing the Overall Systems
Convenience for Servicing


Electrical and plumbing systems comprise the heart of a vessel's operating systems, and because we are dealing with boats that float in salt water, it is imperative that such systems utilize the highest quality materials and be designed and installed by competent professionals. Therefore, this chapter will give you a detailed overview of these systems.

The good news for later model boats is that they don't have anywhere near the kind of electrical problems that they had only fifteen years ago.

One reason is that electrical systems have become much simpler in overall design but, unfortunately, that also often means a lot less flexible. Another reason is premanufactured panels that more or less cause the builder to follow a preconceived scheme. Still another is that industry seminars have been helpful in better educating builders, designers and installers about basic standards.

As demands for electrical power continues to increase, the ability of most 125 VAC to meet those demands declines. Twenty years ago, many boats in the mid size class had multiplex high voltage systems. A duplex system is one that has one shore power line plus a generator; a triplex system two 125 VAC lines plus generator. Moreover, a boat's internal system may have, one, two or three legs. That is, certain items of electrical equipment can grouped into circuit A, B or C.

A multiplex system is one that allows us to choose which power sources operate which branches of the system.

For example, let's say we have shore power line #1 line #2 and we have the generator. This gives us a boat on which half of the electrical equipment is on one line, the other half on the other. With a pair of rotary switches, it is possible to wire the system so that we can switch between power sources for any circuit. We can put all on generator, all on shore, or one line on each, shore and generator.

The advantage of such a system arises at those inevitable moments when either the dock doesn't supply enough power, or there are not enough dock outlets are available for us to plug in both lines, and so on. Thus, one leg could be run from shore, the other on generator. This kind of flexibility is a great thing to have since while cruising, it is common to run into problems of inadequate shore power.

Unfortunately, for lower end boats, this degree of flexibility has been decreasing, rather than increasing. That's because sophisticated electrical systems are expensive and builders of "price" boats can cut costs by skimping. When it comes to mid size cruisers with relatively high power demands, it's far better to have two 30 amp, 125 VAC lines than a single 50 amp, 125 VAC line. With the single 50 amp 125V line (which is what we are seeing with increasing frequency) we've got 20% fewer amps (50 versus 60), plus we are reduced to reliance on only a single power source.

cover art: Boat two bows Mid Size Power Boats
- A Guide to Discriminating Buyers

Soft Cover
512 pages
Publisher: D. H. Pascoe & Co., Inc.
Published: 2003
Language: English
ISBN-10: 0965649636
ISBN-13: 9780965649636

Price: $24.50
In Stock



David Pascoe - Biography

David Pascoe is a second generation marine surveyor in his family who began his surveying career at age 16 as an apprentice in 1965 as the era of wooden boats was drawing to a close.

Certified by the National Association of Marine Surveyors in 1972, he has conducted over 5,000 pre purchase surveys in addition to having conducted hundreds of boating accident investigations, including fires, sinkings, hull failures and machinery failure analysis.

Over forty years of knowledge and experience are brought to bear in following books. David Pascoe is the author of:

In addition to readers in the United States, boaters and boat industry professionals worldwide from over 70 countries have purchased David Pascoe's books, since introduction of his first book in 2001.

In 2012, David Pascoe has retired from marine surveying business at age 65.

On November 23rd, 2018, David Pascoe has passed away at age 71.

Biography - Long version