The following is a guide and pertains to the services of J. Simpson Ltd. The policy of other design firms or Naval Architects may differ.

Speed Estimates
Propeller Sizing
Stability Evaluation
Sailing Vessel Rig and Sail Plan
General Arrangements
Structural Details
Weight Estimates
Seakeeping Improvements
Design Check
On-site Consultation (Owner's Representative)


The following is a brief description of some of the most frequent types of consultation we provide to the marine industry. The contents of the subjects addressed should be considered as ‘non-inclusive’ in that each vessel must be reviewed on its own merit. Limiting work to rigid formulae might not be in the best interests of the client or the vessel.
Although we will work on designs other than our own, we strongly recommend that questions and services should be addressed by the original designer of your boat. If for some reason this is not possible, we would be pleased to assist. Out of courtesy, we may request authorization from the designer unless there is a compelling reason not to do so.

Speed Estimates

You want to know if your boat can go faster or how fast it might go with a new engine.
We have standard forms available and with complete information we can predict the speed of your vessel. Accuracy is often within 10% and sometimes 5%.
The most 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 reasonable adjustment of the propeller would make the boat go faster.

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 or cruising in higher risk conditions a thorough review of the stability can be valuable and reassuring. In addition to the initial, stability we also look at the range plus other matters that might limit or compromise stability. For standards we use several criteria with one being 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 will invariably self right after a 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 roll-over) 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 we can review and furnish the appropriate information and drawings.

General Arrangements

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

Alternate or new details to satisfy special needs or requirements. Sometimes a part or detail shown may not be available or suitable. We can offer suggestions and guidance.

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 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 and has weight (mass) must be accounted for. This includes often over looked items like paint and in the case of plates on metal boats, over-rolling. We have had the privilege of reviewing designs in which 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 his boat will be 40% to 60% heavier than quoted and float 8” to 12” lower in the water.

Sea-Keeping Improvements

In an existing vessel, improving the way it handles is sometimes very difficult. Sometimes the problem can be attributed to the design, sometimes the way in which the boat is outfitted. A thorough evaluation of the vessel may offers some clues as to how problems can be lessened, if not eliminated altogether.

Design Check (a second opinion)

This is a review 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, is probably not necessary.
How do you know if a design check is warranted. Even to the untrained eye, sometimes a small item can stand out. A good example is a client who questioned if a ¼” plate deck was needed on his 58’ 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 1700 pounds of topside weight.
Obviously, the “check” is done by someone other than the designer of the work under review. For this and other reasons, some designers may not appreciate their work being scrutinized by others who, in most cases, would be the competition.
While the design check is not commonplace in 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 from a qualified person. After all, it’s your money, your boat, and your life: a good design it will 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 must approve all work and be kept informed of the vessel’s status.