Definition
The hull is the watertight structural body of a vessel, comprising the bottom, sides, transom, deck, and the internal framing that ties them together. It excludes the superstructure (cabin, helm enclosure, arch) and any rig. In tender and chase-boat terms the hull is the boat's defining engineering element; almost everything else is replaceable.
Background and use
Hulls fall into three primary categories by the way they move through the water. Displacement hulls push water aside and travel at speeds limited by their waterline length; rare in modern tenders but common on classic yacht tenders and on some support vessels. Planing hulls lift onto the surface of the water above a threshold speed and ride on a small wetted area; this is the standard tender and chase-boat configuration, with deadrise, beam, and weight distribution governing behaviour. Semi-displacement hulls bridge the two, running efficiently at intermediate speeds and capable of reaching planing speed at higher fuel cost.
Construction material divides hulls again. GRP (glass-reinforced plastic) dominates production builds. Carbon composite is the premium choice for weight-critical work. Aluminium is favoured by some chase-boat builders for impact tolerance and repairability in remote locations. Wood-epoxy persists on classic restorations and a few specialist yards. Steel is rare at tender scale, though common on larger support vessels.
Hull design choices ripple through every other part of the boat. A given hull form will accept certain engine packages but not others, will fit certain garages but not others, will perform in some sea conditions and disappoint in others. Owners specifying a tender from scratch should fix the hull form before agreeing the topsides, electronics, or interior fit; reversing that order is the single most common new-build regret.
Related considerations
- Hull form is the hardest thing to change; specify it for the boat's primary mission, not the marketing brochure.
- Survey hulls in and out of the water; structural assessment requires both views.
- Replating, recoring, and major laminate repair are possible but expensive; price into used purchases.
- Deadrise, beam, draft, and waterline length together describe hull behaviour; no single number suffices.
- Hull-to-deck joint is the highest-risk leak point on any production tender; inspect carefully.