Quote:
Originally Posted by Billybob
Interesting, so how and when did the hulls change up until they stopped making them?
For example is a 2005 designed for a heavier 4 stroke, does it get up on plane, does it bail?
Or something like this - 1986 with a 4 stroke 150 - how would this perform?
I'm just wondering if the 20 design ever evolved to accommodate the newer, bigger engines and how they achieved that. . .
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I can only speak for the SeaCraft “20 ft” hull and I assume that’s what you’re referring to. The hulls DID NOT change significantly over the years from when Moesly made the first
19’ Bowrider in 1965 to whenever Tracker stopped making them! The changes made to that hull that I know of are as follows:
1. The 19 & 20 hulls are identical below the waterline. Moesly made the 20 from a 19 mold by literally taking a chainsaw to the mold! The 19 is a wet riding boat, and Carl Kiekehaefer wanted a slightly longer boat to enter in a 20’ racing class, so Moesly simply cut the mold down the stem to the chine and then back along the chine to amidships. He then moved the hull sides outboard about an inch, creating the spray deflecting flat you’ll see at the chine on the front half of all the 20’s, which disappears about 10’ fwd of transom. He also rolled the hull sides outward to create more flare, and added the clipper bow to tie them together. The resulting hull measured 19’8” on the centerline, which was was evidently close enough to be considered 20’ for the racing class! This became the hull which was the basis for all Moesly and Potter “20 foot” models, including the SF, Seafari, Sceptre and Master Angler. The Seafari is the heaviest of the bunch at 1800 lbs for the outboard bare hull, with most of the weight of the cabin top and raised coaming, windshield, bunks, head, bulkheads and cabin door being forward of the fuel tank, so it’s a bit less stern heavy than the CC models and therefore able to handle a heavy motor better than the other models.
2. Potter raised the cockpit sole a couple inches in about 1973-74 when he changed from the 4 narrow stringers to 2 wide box stringers, but this basic hull continued in production until Potter went bankrupt and sold the molds to SeaCraft Industries about 1980. The ~350-375 lb V-6 motors (Merc Black Max and OMC 90 degree cross-flow motors) came out in the late 70’s, and Potter started offering the full height splash well tub as an accessory and included a full height design on the MA, so he was obviously aware of the reduced transom freeboard due to the extra weight.
3. I have a SeaCraft Industries brochure from 1982 which indicates the transom height was raised to 25” on all models, and centerline length had been increased 8” to 20’4”, but beam remained unchanged at 7’6”. They only made CC models which all had full height splash wells, with a revised transom containing storage boxes/bait wells similar to the Potter MA models.
Other than a length increase of a little over 3%, raising the transom from 20 to 25”, and moving the scuppers to drain out the transom, NOTHING has been done to the basic hull design on the later Tracker models to allow them to support the weight of a much heavier 4-stroke motor! This is why, after personally discovering the negative impacts of the “Aft CG shift” on my Seafari after adding a 30” setback bracket and a much heavier motor, that I have continued to emphasize for the last 10 years that “Light is Right” on the 20’ hull,
especially when adding a bracket!
On CC models, you do have the option of moving the batteries into the console and moving the console forward to minimize the CG shift caused by a heavier motor. Depending on it's size, you may also be able to move the fuel tank forward. How far to move the console can be determined by doing a simple moment balance if you know the weight of all the components being moved. It's safe to assume that the CG was at the center of the fuel tank with a 300 lb motor on the transom and a single battery at the transom in the original design.
Bottom line: the design was
NEVER “evolved” (some would say screwed up!) to accommodate newer, heavier engines, so if you’re contemplating any motor over about 400 lbs, think it through very carefully! Any naval architect will tell you that one of the most important parameters of any boat design is the location of the CG, in both fore & aft and vertical dimensions. So if you’re thinking of installing a 4-stroke motor and/or a bracket, where motor weight is even more critical, be prepared for min planning speeds in the low-mid 20’s instead of about 12 mph that all the Moesly designs would do with original power! And don’t expect the amazingly soft ride and efficient performance that these boats quickly became famous for with the relatively small motors available back in the 1960’s and 70’s!