Amphibious Tender Design • Seastead Support

Existing Amphibious Boats (9–14 ft range)

Very few true 9–14 ft amphibious tenders exist on the market. Most amphibious boats are either:

Sealegs / Iguana style (3.5–5m+): $80,000–$180,000. Heavy (400–900 kg), complex hydraulic legs or tracks.
Small tracked RIBs: Mostly custom or military. Rare in civilian market under 14 ft.
Jet ski conversions with tracks: Exist but not practical as a 4-person tender.

Conclusion: No mainstream, affordable 11 ft amphibious tender currently exists. This represents a genuine market gap.

Skip complex tracks. Use the shape of the hull + a small electric winch + anchor.

Rotomolded HDPE catamaran hulls with a gently curved bow and flat bottom section
Small 12V electric winch (1,000–1,500 lb capacity) mounted on the tender
Lightweight folding anchor or sand screw
Operator places anchor 25–30 ft up the beach, then the winch pulls the boat ashore

Advantages: Extremely reliable, almost zero moving parts in sand, very low cost, easy to maintain.

If you still want self-propelled movement:

Tracks are prone to sand jamming and are mechanically complex. Wheels or the winch method are strongly preferred.

Floats: Rotomolded HDPE (linear low-density polyethylene) – excellent UV resistance and impact strength
Cross beams: 80/20 aluminum extrusion or 2" schedule 40 aluminum pipe
Deck: Marine plywood with non-slip coating or aluminum grating
Winch: 12V ATV-style winch (Warn or generic Chinese equivalent)
Outboard: Yamaha HARMO or equivalent electric

Best balance of cost, durability, and waterproof integrity for low-volume production. Can include internal baffles for strength and mounting points.

Item	Cost (USD)
Rotomold tooling (one mold set for both pontoons)	$8,000 – $12,000
Aluminum crossbeam tooling / fixtures	$1,500
Per-unit manufacturing cost (20 units)	$1,850 – $2,350
Total landed cost per unit (20 units)	$2,400 – $2,900

Includes: rotomolded pontoons, aluminum structure, deck, winch, basic wiring, and packaging. Does not include electric outboard or batteries.

Typical cost for a custom aluminum rotomold of this size (11 ft pontoons):

Common first-run size for rotomolding is 500–2000 liter capacity. Your pontoons fall comfortably in the mid-range.

Go with the winch + sled design. It is dramatically simpler, more reliable in sand, and cheaper to produce and maintain than any tracked system.

Target retail price: $5,900 – $7,500 (including electric outboard). This leaves healthy margin after manufacturing and shipping.

This product has strong potential as a niche seastead / expedition tender because no direct competitor exists at this size and price point.