|Posted: September 09 2007 at 16:42 | IP Logged
I Have '83 Catalina 280 with the single 308. Standard for the Model.
For our boat, we found that when we started using her, the driveline was a symphany of noises. First, Back filling and redrilling the shaft log bolt holes was required. CC got it wrong on our boat. Fortunately, our drive-line Guru spotted the misalignment while hauled out. One noise eliminated. Then, there was cavitation and she was turning too many RPM's with too low a speed. We went from a 16" to a 15 3/4" prop to move the prop tips away from the hull eliminating cavitation and our prop guy steepened the pitch...problems solved, nice and quiet.
CC made a comprimise between performance and economy and the 308 is right at it's max power to weight ratio with moderate people/provision/fuel/water loading and using trim tabs (which was not standard equipment). By the book Maximum RPM specification is 4400 RPM WOT. She should get on plane by thottling up to 4000+ RPM and gradually kicking in the trim tabs once she gets to 8-9 knots. Once she was on plane. I backed down to 3400/3500 RPM and adjusted the tabs. The engine works pretty hard and it's loud, but she rides well enough and was doing 12-14 knots, maybe a little more if pushed. This does wear the engine. If you go with the 308, special attention to maintenance will help deal with that wear. If you go over her power-range due to over-weight, the engine will backfire, miss- basically complain... back off the throttle and the engine smooths out. As an illistration, Adding 50-70 fuel gallons of added weight made the differance and made the engine hesitate when we were trying to get back on plane- we backed off and took it easy till the fuel tank was half full then took off again, no problem.
At throttle up/on plane I was getting maybe 12 to 14 gph. At off-plane speeds of 8-10 knots- 6-8 gph- and by the way, this is where we typacally run her.
For regular on-plane use, I'm thinking GM 350 adds 55 HP. The cool thing is that the 308 and 350 use the same footprint and a lot of parts are interchangable, including the gear/transmission. A long block of the same year/series would do nicely.
Fair winds, following seas, Roy
Roy & Laurie, S.F. Bay Area
'83 280, hardtop, single 305