Below is a detailed response to your query about the seastead's emergency propulsion using a dinghy equipped with Yamaha Harmo motors. I've addressed each point based on available information from Yamaha's specifications, general marine engineering knowledge, and online searches for suitable boats. All estimates are approximate and should be verified with professionals for safety and feasibility.
The Yamaha Harmo is indeed a rim-drive electric outboard with impressive efficiency, boasting a high thrust-to-power ratio of about 61 lbs/kW (227 lbs thrust from 3.7 kW). This is excellent for static/bollard thrust applications like towing.
Have I seen any more efficient? Based on comparisons:
If you're looking for alternatives, consider the Elco EP series, but they might not beat the Harmo's ratio.
Yamaha officially supports "twin mode" for two Harmo units, allowing synchronized control via their Helm Master EX system. This integrates steering, throttle, and joystick functionality for easier maneuvering.
For three units: It's not officially supported out-of-the-box, as Yamaha's documentation focuses on singles or twins. However, it's feasible with custom integration. You might need to contact Yamaha or a certified dealer for a multi-engine setup. Systems like Helm Master EX can often be expanded (e.g., for triple or quad outboards on larger boats), but it would require custom wiring, software configuration, and possibly additional controllers. Expect potential extra costs and engineering to ensure balanced thrust and steering.
Yamaha lists the control system as "Helm Master EX, including joystick, remote control, and Digital Electric Steering (DES)". Here's a breakdown:
These components make the Harmo highly controllable, especially for emergency towing.
Three Harmo motors would provide approximately 681 lbs (3 x 227 lbs) of bollard thrust. For a 30,000 lb seastead with a non-hull shape (like a small oil platform with high drag from columns and cables), movement would be slow.
Do I agree it can move at least 0.5 MPH in no wind? Yes, in calm conditions, this seems plausible. Rough calculations (using drag estimates for semi-submersible platforms) suggest 600-700 lbs thrust could achieve 0.5-1 MPH on flat water, assuming efficient towing setup. Factors like currents, wind, or waves could reduce this significantly. Real-world testing is essential—consult a naval architect for precise modeling.
Powering via a cord from the seastead is viable for hours if your battery/solar setup can supply ~11 kW continuous (3 x 3.7 kW).
The Harmo's control system uses digital cabling (likely CAN bus or proprietary Yamaha wiring) for steering, throttle, and diagnostics. It's not a simple "cord" but a harness that connects to the helm controls.
Can it be made longer? Yes, extensions are possible. Yamaha offers extension kits, or you can use marine-grade cables (e.g., up to 50-100 feet) with proper shielding to avoid signal loss. For unmanned dinghy operation, you'd route controls to the seastead's helm. This could work with Helm Master EX's remote capabilities, but ensure waterproofing and safety (e.g., kill switches). Consult Yamaha for compatibility to avoid voiding warranties.
Yes, this plan looks reasonable as a backup propulsion method. Using the dinghy as a "tug" leverages its wave-following ability, avoiding submersion issues on the seastead (a smart point you noted). With three motors, it provides redundancy and sufficient thrust for emergencies. Storing extras on the seastead is practical. Potential improvements: Add towing bridles for stability, ensure the dinghy's transom can handle the weight/thrust of three motors (681 lbs thrust + motor weight ~300-400 lbs total), and test in controlled conditions. Unmanned operation via extended controls is feasible but adds complexity—consider wireless options if available.
Risks: High drag could strain motors; ensure cooling and overload protection. Legal/safety note: Comply with maritime regulations for towing and unmanned vessels.
I searched for "HDPE boat", "rotomolded polyethylene boat", "PE fishing boat", and "rotomolded utility boat" in the 4-5 meter range from Chinese manufacturers (e.g., via Alibaba, Made-in-China). These are durable, lightweight, and corrosion-resistant—ideal for your dinghy/tug needs.
A suitable match: A 4.5m rotomolded HDPE utility/fishing boat. These can often handle multiple outboards if the transom is reinforced.
Note: Prices fluctuate; contact suppliers for customizations like reinforced transoms for triple motors. Shipping from China adds $500-1,000 depending on location.
If you need more details or refinements, let me know!
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