Drop Fins and Propspeed

Similar experience to BBMarine - C26, Yanmar 4BY2-180. Installed the drop fins and the Mente auto-trim, delighted with results. have seen 26 mph under perfect conditions but ordinary top end is around 20mph. And - there's definitely a bit of overkill, fully deployed tabs seem to lose control of the inherent list-to-port and give an unstable bow-steered ride at high speeds.

/tmm

Titanium and cutting oil. I'll give it shot on next haul out. Thanks.

a little bit unconventional I first started to drill the drop fins and even with cobalt drill bits I said forget it. So I lined up the drop fins clamped them in place and spot welded them to the tabs. This is year 3 and have no issues from that. Also
painted the prop with a barrier coat then two light coats of regular home depot cold galvanizing zinc paint. Its been mentioned many places on the internet. Funny thing it worked quite well. Not too bad for around 10 bucks a can.

Stuart

too bad the photo area isn't working, I built a suitcase fuel polisher and wall able to clean some sediment/sludge through opening after removing the fuel sending unit. Did not find any water in the separator and it frees up the onboard filter not having to work as hard.

I just went to HD and bought 1 size bit larger than the screw I used. I bought the advertised "hard" bit, I think it was the milwaukee brand. I dipped the bit in a cup of oil before each attempt . Laying on my back with some eye protection using a cordless drill I put 4 holes per side 8 total per fin. I think start to finish was less than an hour . I predrilled the fins first and clamp them to the tabs. My problem is the boat is to far forward so the fins will hit the bunks on the trailer. When we hauled the boat in the fall I purposely left it 4 inches back from the winch stop. I still think I have plenty of Tonge weight. I use the trailer for storage. If I ever decide to take it any distance I will have revaluate.

I was surprised at how well those Harbor Freight step drills work for drilling stainless. Drill a very small pilot hole, usually pretty easy with sharp bit, then the step drill to enlarge. Cuts very easily. I am not generally a fan of Harbor Freight, but these work well. DS

Just a follow up on this C-28 trim tab issue.
After a full season of use (90 hours) I’m glad I upgraded to the larger 12x18” trim tabs. To keep the bow reasonably down I’m using full down trim tabs at cruising speed with our heavily loaded boat. I measured the max deflection of the trim tabs while on the trailer and found it only to be 21 degrees or about 4 3/8” of travel as measured at the trailing edge. This is much less deflection than the trim tabs on our R-25 Classic. I’m guessing is that this is due to the actuator being attached further aft on the C-28’s trim tab and/or the top of the actuator being mounted higher on the hull than it was on the R-25.
I’m going forward with installing the drop fins. My goal is to be able to properly trim the bow at cruising speeds without maxing out the trim tab deflection every time.

I have a C 28 with a 25 hp Yamaha on the stern and a 15 gal Gas tank. I have a 1" spacer on the bottom of the trim tab actuator and drop fins giving 12 X 16" tabs. At 3000 RPM, with 3/4 tank of diesel,full water,3 persons I get 2.1 NM/Cdn gal ,17.2 knots with a 6 second count down on the trim tabs. Any more down on the tabs I lose speed and economy.