Center of Gravity

[Capt. Rich]

Pictured are two similar boats. One is a brand new Striper 29' boat with twin Volvo D-4 210hp I/O diesels and an Albin 28 with a single Yanmar 300hp diesel.

Both owners probably paid similar prices for their rigs. Volvo, Yanmar, Albin and Striper do not give away their products. From the bootstripe you can tell that the Striper is very heavily loaded to the stern. In fact the local Coast Guard station has had several calls that the boat was sinking.

I find this to be very distressing. Obviously the Striper owner bought his boat believing that he was getting the best rig to chase tuna. I understand that he has all the bells and whistles installed. But the manufacturer has forgotten the basic rule of boat design. Even keel. Albin obviously has designed its boat with this engineering priniciple in mind.

Related posts on this thread talked about porpoising and bow steering. I would venture to guess that this Striper will suffer from porpoising. Porpoising in a boat is directly related to the center of gravity. If the center of gravity is not near or slightly aft of the center of the boat, a boat will porpoise. Too far forward and it will bow steer. No amount of trimming by trim tabs will cure these problems.

Good boat building companies like Albin, Bertram, Davis, Farallon, Fibercraft, Parker, Shamrock and others that build great 20-30' boats designed their boats with the center of gravity in mind and would make various models of the same hull design with different engine placement. The Bertram 25 came in several different designs. The I/O version had twin MerCruisers but the heavier Crusader V-8 powered boats were built as inboards with the engines placed further forward.

Volvo makes several models of diesel I/O. The Albin with a single Yanmar 300 hp diesel is capable of a 20 knot cruise speed. Volvo makes a 160 hp I/O that weighs 717# each. The D4 I/O package in the boat weighs 1420# each. Old salts say that diesel horsepower is far greater in real pushing power than any gas rated horsepower. Something to do with the torque and fuel effiency of diesel fuel.

I would venture to say that if this boat were equipped with twin 160hp diesels at a loss of 1400# off the stern, this boat would handle better, get great fuel economy and would probably go only slightly slower than it is presently configured.