Sea Trial

A conversation among Whalers
Keyaskom
Posts: 14
Joined: Sun Apr 17, 2022 6:51 pm

Sea Trial

Postby Keyaskom » Mon Apr 18, 2022 9:15 am

During a seal trial [of a 53-year-old Boston Whaler boat which has been extensively modified] what specifically should be looked for?

jimh
Posts: 11673
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Sea Trial

Postby jimh » Mon Apr 18, 2022 9:25 am

With regard to the engine, a sea trial should establish:
  • the engine starts easily; an older two-stroke-power-cycle in proper tune should start on the first or second attempt with very little cranking
  • after starting, the engine idles at an appropriate speed and does not stall
  • the idle speed adjusts for the engine temperature, idling faster while cold and reducing idle speed after warm up
  • the engine shifts from neutral to forward or to reverse without difficulty, without clashing of gears, and without loud noises
  • the engine is able to accelerate to an engine speed which produces a boat speed that can maintain the hull on plane at an engine speed well below full-throttle
  • at full throttle the engine can accelerate and maintain an engine speed within the manufacturer's recommended full-throttle engine speed range, preferably in the upper quarter of the RPM range; and
  • the boat speed at full-throttle is appropriate for the boat weight, engine power, engine speed, and propeller pitch
With regard to the hull, a sea trial should establish:
  • there are no leaks or unexpected ingress of seawater
  • the hull in static trim results in a water line appropriate for the hull and weight being carried, with a slight down-by-the-stern trim; a good indicator of proper trim cam be made from judging the position of the engine splash well drains relative to the water line at the transom; the drains should not be submerged
  • in static trim the hull has no prominent list; a slight list to starboard is common and promotes drainage to the cockpit sump, and
  • the hull is rigid and there is no sign of flexing or movement in the hull or transom when the boat is underway at speed and encounters waves.

In order to conduct a proper sea trial, the engine must have a tachometer, and the boat speed must be measured accurately, typically with speed-over-ground data from a global navigation satellite system receiver.

If subsequent advice is to be solicited about the performance of the boat, all of the following information should be provided:

  • Environmental Information
    • name of body of water
    • air temperature
    • water temperature and salinity
    • humidity
    • altitude
  • Engine Information
    • complete model description, rated power, model year
    • gear ratio
    • recommended operating speed ranges
    • maximum engine speed allowed by manufacturer
  • Propeller Information
    • make, model, number of blades, material
    • pitch
    • diameter
  • Boat Information
    • make, model, year
    • length
    • fuel, crew, and gear aboard during test
  • Observations
    • date of the test
    • tabular presentation of engine speed and boat speed, over a range of speeds covering full-throttle to lower throttle settings which still produce boat speeds on-plane
    • instruments used to measure engine speed and boat speed
    • observations about behaviors such as propeller ventilation, bow oscillations, pronounced lists, and similar unusual effects