Note: The following is a guide to our services & policy. Each project will be assessed on an individual basis.

Custom Design

If, after a thorough review, it is determined that a suitable stock plan is not available, the next option is a custom design- a design developed specifically to meet the client’s requirements.

At this time, J. Simpson Ltd. is concentrating services to stock plans, preliminary design, and consultation. If a final custom design is required, the project may be referred to an associate.

The design of a boat is an evolutionary process, often with multiple issues to address at each stage:

  1. Concept Design –get the ideas on paper… a start with basic details- size, material, application, etc.
  2. A Preliminary Design –functional ideas- on paper Drawings, specifications, etc., which can be used for review by all people involved:
    • owner
    • designer
    • builder (for estimate & quotation)
    • third party & sub-contractors: moorage, outfitting, etc

Consultation Services

Some examples

Speed Estimates

You want to know if your boat can go faster or how fast it might go with a new engine.

Standard forms are available and with complete information the speed of your vessel can be predicted.  Depending on accuracy of information furnished, estimates are often within 5%.

One common reason for this calculation is to verify the existing installation. Example: a review of a 42’ planing hull determined that the incorrect reduction gear was fitted and no adjustment to the propeller would make the boat go faster or the installation more efficient.

Propeller Sizing

You may or may not have the correct propeller. This is related to the speed estimate but often the problem can be insufficient diameter (& resulting low blade area) or a poor installation.

Stability Evaluation

If you are going offshore, cruising in higher risk conditions, or a commercial vessel, a thorough review of the stability can be valuable and reassuring. In addition to the initial, stability there is the range of stability and other matters that might limit or compromise stability. For standards, several criteria can be used such as the I.M.O. (International Maritime Organization). Calculations are done for still water only since trying to predict what waves a vessel may encounter is highly speculative and almost impossible.

Self-righting: A well designed, built, and maintained sailing vessel (mono-hull) will invariably self-right after capsize. For powerboats, the configuration of the hull and superstructure is different and self- righting and intact recovery may not be possible. Vessels claiming to be self-righting (positive stability through a 180 degree rollover) will require special attention to the structure, outfit, and interior storage. Arranged as such, items like broken windows, backflooded engine exhaust, and flying interior objects would not be of concern. Unfortunately, such arrangements can be expensive, very invasive, and may detract from the habitability of the vessel.

Sailing Vessel Rig & Sail Plan

Some owners may want to alter the rig (cutter to ketch, etc) or increase its size (sail area). With correct information the appropriate information and drawings can be furnished.

General Arrangements

The owner may need an alternate or new layout to satisfy special needs or requirements. Work may be limited to one area (or drawing) or may encompass the entire boat.

Structural Details

Provide alternative or new details to satisfy special needs or requirements. Sometimes a part or detail shown may not be available or suitable: suggestions and guidance can be offered.

Weight Estimate (Mass Analysis)

As a part of the design process, the weight estimate (sometimes called a Mass Analysis) is a crucial calculation. Unfortunately, it is also tedious and one of the less pleasant chores that a designer must perform. The boat is floating in a fluid and therefor affected by weight. Each and every item that goes into building, equipping, and operating the vessel has weight and must be accounted for.  This includes often over looked items like paint and in the case of plates on metal boats, over-rolling. After reviewing some designs it was quite obvious that a weight estimate was never done, or if done, was perfunctionary at best.  It is not a pleasant task to inform a client that the boat will be 25% to 40% heavier than quoted and float several inches lower in the water. This situation will impact the entire vessel…..propulsion system, stability, and perhaps safety. It is often incurable and carries a hefty penalty.

Sea-Keeping Improvements

In an existing vessel, improving the way it handles is sometimes very difficult. Broaching, excessive weather helm, and chine walking (progressive heeling) can often be attributed to the hull form or the way in which the boat is outfitted. A thorough evaluation of the vessel may offer some clues as to how problems can be lessened, if not eliminated altogether.

Design Check (a second opinion)

This is an analysis of a design in its entirety and may range from a quick revue to a detailed assessment. If a fair amount of time is required, the design check can be a fairly expensive and in the case of a design from a competent designer, probably not necessary.

How do you know if a design check is warranted? Even to the untrained eye, sometimes a small but critical item can stand out. A good example is a client who questioned if a ¼” plate deck was needed on his 54’ steel cruiser. Unless he was expecting heavy deck loads (wheeled traffic, cargo, etc.), the use of 3/16” plate (or possibly 10 ga) would be quite sufficient. This small revision saved him some money and improved the stability by eliminating about 1400 pounds of topside weight.

Obviously, the “check” is performed by someone other than the designer of the work under review. For this and other reasons, some may not appreciate their work being reviewed by those who in some instances would be considered the competition.

While the design check may not be commonplace for small private vessels, it is quite common on government projects involving public (taxpayer) money. If you suspect a problem (or even if you don’t) there is nothing wrong with a second opinion.  After all, it’s your money, your boat, and your life: a good design should stand up to scrutiny.

On-Site consultation

In additional to our own designs, we can also provide this service for clients of other designers. The purpose is to provide some on-site verification that the builder is following the plans, the intent of the design, and good shipbuilding practice. In some cases we might be asked to furnish technical assistance to the builder on behalf of the designer. In all cases the designer will approve all work and be kept informed of the vessel’s status.


We have done several articles which may assist the boat owner or builder. Copies are available for a nominal charge. For a complete list please see the end of this section.

Some Sample Cures

Note: Few cures are 100% effective but do improve the boat to a useable and safe condition.

  1. 33’ power catamaran – tended to chine walk at speeds over 26 knots. Cured
  2. 40’ patrol vessel –  tended to chine walk at speeds over 22 knots. Cured
  3. 44’ cruiser – with twin 300 hp diesels achieved a top speed of 11 knots, engines would not achieve full RPM, over-heated, blew black smoke. Cured- new top speed was 16 knots, engine at proper operation.
  4. 56’ Offshore cruiser – broaching, high roll angles. Cured. Customer did a return trip from Mexico to Alaska & no longer terrified.
  5. 44’ aluminum sailboat – maximum speed under power was 4 knots. Cured. (poor propeller installation)
  6. 40’ power boat-customer want better maneuvering in tight quarters – cured