TOW BOAT

Passage Maker - - From The Pilothouse -

We will be re­tir­ing soon and pur­chas­ing a small trawler to cruise the Ba­hamas. We have been trai­ler­ing a small Grady-White out­board (weigh­ing about 2,500 pounds), and run­ning it from West Palm Beach to Hopetown, Abaco, ev­ery year. In the near fu­ture we plan on towing this same boat from Bal­ti­more to the Ba­hamas with our trawler. I will beef up the bow area of the Grady to make it suit­able for towing, but my ques­tion lies with the trawler.

We are cur­rently look­ing at a Main­ship 350 with twin diesels. Towing the Grady will cause not only a de­crease in speed but also a change in the Main­ship’s rpm. As this is a long tow, I want to make sure we are run­ning as ef­fi­ciently as pos­si­ble, as well not harm­ing the en­gines. First, can this be done? And sec­ond, if fea­si­ble, then I am think­ing of two sets of props. One set for towing, and an­other set for our months of cruis­ing in the Aba­cos. This would also pro­vide us with a spare prop for each shaft, even if not the same pitch or di­am­e­ter.

Can you val­i­date or of­fer other ideas or sug­ges­tions? Joe Bor­ri­son Rockville, Mary­land There are some vari­ables to con­sider be­fore ex­press­ing a com­plete opin­ion on this ques­tion. The an­swer hinges mostly on the mo­tors. Older, me­chan­i­cally timed en­gines were de­signed to run at a nar­row range of rpm and load. In this case, it would not be good if you could not reach cruis­ing rpm but the mo­tor re­mained un­der high load. In this in­stance, I would look at the ex­haust for black smoke, sig­nal­ing that the amount of fuel supplied is not be­ing burned, be­cause the en­gine speed is not high enough. Also, I would ex­pect that the oper­at­ing tem­per­a­ture would be ris­ing. If, on the other hand, you are able to reach rpm and the en­gine is not smok­ing black or get­ting be­yond the oper­at­ing temp as spec­i­fied by the man­u­fac­turer, towing may be fea­si­ble. Re­mem­ber that fish­ing trawlers pull great loads with­out prob­lems as well as trav­el­ing long dis­tances with­out towing loads.

If the en­gines are com­puter-timed mod­ern en­gines and of suf­fi­cient horse­power, I would think the idea a bit more fea­si­ble as the en­gines can run un­der a greater range of loads and rpm with­out dam­age. In ad­di­tion, mod­ern en­gines can ac­cu­rately mon­i­tor load per­cent­age, fuel burn, and boost pres­sure to as­sess whether the load is com­pat­i­ble with the propul­sion.

To ad­dress the ques­tion di­rectly, I do think it is pos­si­ble, al­though it would re­quire ex­tra dili­gence con­cern­ing weather and fuel range. I do not much like the idea of re­siz­ing the props for towing, as you would be de­creas­ing pitch to in­crease en­gine speed. This could have dra­matic con­se­quences in ex­treme con­di­tions. Again, this all de­pends on the horse­power avail­able, so no rea­son­able an­swer is pos­si­ble with­out more in­for­ma­tion and some live test­ing at sea. Capt. Larry Crouch Galve­ston, Texas

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