Why do I have so little power when backing (in reverse)?

I am experiencing great difficulty motoring in reverse (at the docks ). The rudder takes forever to bite and the situation gets worse with windage. The boat has a 33 HP Vetus ( underpowered in my opinion ) and swings a 18″ three blade fixed prop. Come haul out, I will be considering adding 6″ or so to the rudder, maybe a different prop. and eventually I will be upgrading to a larger engine before heading South. Any comments and / or suggestions on motoring this boat would be much appreciated, before serious funds are spent in correcting this problem. Regards, Frank Bryant, (s/v #186, Visitant, # 186)

a. I assume that your boat has factory rudder–don’t touch it–there is no problem if it is. i had the same problem with my boat– Westerbeke 33 (same setup as the Vetus. the problem is that the engine is on the low end for the displacement– I repowered with a Yanmar 4jh2e (50/51 h.) naturally aspirated. I have a 3 bladed fixed prop 18″ repitched to 14″– great reverse thrust and control (don’t be afraid to add a little power in reverse, all the while keeping control of the rudder so that it does not swing to one side with the boat motion. fyi, Marius Corbin repowered his (now sold, Stradimarius II, #129) with a Vetus 50hp in 1985– to get more power and speed– think he went to a feathering prop, 18.” Doug Archibald (#158, Chaos !! #153).

b. I too would be interested in solving the reversing problem in the Corbin. I have a feeling the rudder is not effective enough in reverse, perhaps in forward too. The trailing edge is quite thick and I think to extend it rearward would add a considerable amount of area. Another approach would be to cut off some of the skeg area and move the lower rudder bearing up and do a partially balanced rudder. As it is, there is quite an area of the rudder, however ineffective that backing down puts a strain on the rudder if going too fast. I have a Perkins 4-108 that seems appropriate for the boat with an 18-inch fixed three blade wheel. The pitch escapes me however. The engine runs at 2600 rpms max. and it is rated at 3200. The cruising speed seems to be 7.5 knots, max in smooth water is 8.2 knots. How many Corbins are using a V-Drive ? Does the prop walk move the stern to starboard ? Gene Whitney (#069, Joint Effort)

c. I have a Volvo 34 hp diesel driving a 15×13, 3 blade propeller with a sail drive (ratio 1:1.66) and only have minor backing problems to starboard. I find that if I rev the engine over 1000 rpm I have less paddle wheel effect. My top speed seems to be only about 6.5 knots in calm conditions and the engine revs to about 2200 (rated at 2500). Hope this helps. Bill Schwartz (s/v #090, Moonshadow)

d. I have the same problem with my Pathfinder 50 (40 HP) driving a 18″ x 12″ (?) 3 bladed prop. The prop walks to port in reverse (same direction as engine rotation) so the boat won’t steer to starboard unless there is a good deal of way on and that takes space, time and bravery. I think it is also a function of the long keel as I experienced the same thing on a previous 28 ft boat that had a balanced rudder and no skeg. The balanced rudder has a very strong tendency to whip over if it gets slightly out of dead ahead. On my Corbin I didn’t like the flat profile of the original rudder halves so before assembling it I made plywood sections attached to each of the stainless steel web pieces to fatten the curve. I also inserted a stainless steel plate the full height of the trailing edge, extending about 1″ from the rudder. This gave a more tapered aft end and a slight increase in area. None of this seems to cure the backing up problem but it might have helped the water flow across the rudder going forward. I should add that the rudder is filled with solid fibreglass resin putty so it is heavy but rugged. The large volume almost went off (catalyzed) before we could bond the two halves around the rudder stock! David Salter (s/v #050, Opportunity)

e. Frank, here are some URLs for Autoprop, www.autoprop.com and www.pyacht.net/ . You can call or email them and get a quote for your engine. Do not modify your skeg or rudder as these are designed for moving the boat forward. Lester (s/v #010, Insouciance)

f. I have just installed an Autoprop. It has virtually eliminated propwalk, and I can actually drive the boat astern in complete control. Amazing!! On trials we achieved a speed of 8 knots at 2600 rpm at 2200 rpm we can maintain 7 knots….amazing!! It has put a big strain on the drive train though, and I will be rebuilding the Vetus coupling and installing a new bearing in the thrust block…both are complaining! Altogether though this add on has made an amazing difference to the boat.I cant wait to see the fuel economy figures. Jeremy Parrett (s/v #101, Pelican 1 / Two Pelicans)