Getting the tow where it needs to go

May 25, 2022 by JD Anson

Power load, weather conditions, and size of the mothership are only a few of the factors that must be considered.

Drag a large tender behind a 164-foot (50m) motor yacht and it is hardly noticed, but pulling it behind a smaller yacht or sportfish creates a whole new world of challenges. Many smaller yachts and sportfish are designed to cruise at a relatively high speed compared to the typical tri-deck. Adding several tons of drag severely impacts fuel economy, as well as seakeeping ability.

Because of these concerns, many tenders are run on their own bottom for passages. Weather conditions that may be annoying to those comfortably on board a yacht can become downright dangerous when traveling in a small craft. Navigation at night is much more difficult, and tenders simply do not have the range of a large power yacht. Also, manning needs require a minimum number of people on board both vessels, but many yachts do not have qualified spare crew to operate two vessels over long range.

Towing a tender behind smaller boats can create seakeeping issues. Sportfishers especially have very low transoms. In large following seas, the drag of the tender can cause swamping of the cockpit. Though once or twice may be OK, repeated flooding can overwhelm the small bilge pumps usually tasked with keeping the bilges dry, causing the mothership to ride lower in the water and become more susceptible to further swamping. Keeping the vessels in sync with the waves — i.e., both vessels on wave peaks at the same time — can help reduce the danger. This requires constant monitoring and trial to find the best solution of speed and hawser length for the tow and sea conditions.

Some yachts have shipped the tenders in advance to where they will be cruising. This is inconvenient since the tenders now cannot enter customs as part of the yacht. Transit times for the yacht and the ship are different, thus requiring logistics help on both ends. And it is costly, as a transport cradle usually has to be custom-built and shipping costs are high. The cradle will then need to be stored until its next use.

Low-tech polypropylene towing hawsers have given way to ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) commonly known as Spectra and Dyneema. This exceptionally strong line reduces storage room, is lighter, and is highly abrasion-resistant. With a specific gravity of 0.97, it floats on water to help avoid fouling propellers when retrieving the tender. However, it has very high lubricity, which makes for poor knot-holding capabilities. These towlines and bridle lines are best professionally made up with splicing and sewing.

These days, behind nearly every yacht, we see the latest and greatest tender in tow. They feature an endless inventory of equipment, but it is the engines that first catch one’s interest. What kind are they and how many?

For tenders equipped with engines manufactured outside of the U.S., there are a number of regulations that must be met. These rules are primarily outlined in the Code of Federal Regulations, Title 40. They are enforced by the U.S. Environmental Protection Agency. The EPA has adopted exhaust emission standards for both marine gas and diesel engines installed on a variety of marine vessels. They range in size and application from small recreational vessels to tugboats and large ocean-going ships.

For these engines to be allowed into the U.S., they must be in compliance with the Clean Air Act. Certain exemptions are permitted for older engines, special types, and display models.

For diesel engines manufactured after January 2000 and above 130kW in power, a specific document will be issued by the manufacturer to verify compliance. Known as the Engine International Air Pollution Prevention, or EIAPP, certificate, this document is internationally accepted. It confirms that a specific engine meets the NOx emission limits for diesel engines as set out in MARPOL, Annex VI, Regulation 13. - Capt. Jake DesVergers

The advent of AIS (automated identification system) transponders now allows real-time location of the tenders should they become detached from their towing hawsers. Each transponder has a unique identifier that is programmed into it and displays vessel name and position, making relocation of lost tenders quicker. Beware a common mistake when commissioning AIS: using the yacht’s identifying number. Each vessel has to have a unique number, easily obtainable through the flag state. Using the yacht’s AIS number with an “a” at the end is acceptable, but only for tenders carried on board – not for towed tenders.

Ensure there is sufficient power available for the lads on the tender. The best solution is a dedicated house battery just for the loads necessary for towing configuration. Coupled with a properly sized solar panel mounted on the hardtop, this will keep the lights on happily over many days. If there is no room for this dedicated battery bank, a switched “tow” circuit can be designed that removes all loads except the necessary ones from the house batteries. This will extend the power life of the batteries to hopefully reach port. Some tenders have included a spreader light that will activate with a high-water alarm to alert those on board the mother ship that there is an issue.

Many panels we have seen are woefully undersized. One must consider not only the load, but factor in cushion for cloudy, rainy days when production is nil. Stated wattage ratings are for perfect conditions and the testing procedures can be a bit dubious. Take all declared specifications with a grain of salt.

Good planning and weather forecasting are essential to getting the tow where it needs to go.