F26 prop sizes

[foofer b]

I recently bought a 1978 F26 hard top (flybridge removed actually). It has a single chvy 454 raw water cooled inboard, a repower I believe. I think it has the original shaft and prop. I think it needs more prop, but I have not been able to hit WOT because of excessive vibration above 3600 rpm, due to shaft wallop ( I guess). After having 2" more pitch added to the prop ( to 14x19" x1"-I think-have it written down somewhere!) she runs about 17-18 knots at 3400 rpm. From a stop the engine revs up far too readily to 3000 rpm before she starts to bite in. My questions then are Did the F26 FB ever come with a 454? and what size prop should I get? Any suggestions and advice would be greatly appreciated. Plus where can you get a used prop on the cheap? Finally, how do you post your pic with your replies?

[MattSC]

I don't believe that they ever came with a 454. I know they came with a chrysler 318 (225 hp) or a mercruiser small block (233 hp).
As far as your prop, what transmission do you have on the boat. (for example I have a borg warner with a 1:1 ratio. I repowered several years ago with a 5.7 liter fuel injected crusader which is rated at 330hp. I have a michigan dynajet 14x10" propeller with a full cup. I reach my maximum rated rpm which is 5000, I think a 454 should be around 4200-4400. I cruise 17 knots at around 2900-3000 rpm. WOT will get me 31knots. Your vibration could be several things, engine alignment, shaft, or the prop could be out of balance. When I was testing props, I noticed that without the cup, the prop would slip and not bite the water. The cup made a huge difference for me. Good luck
Matt

[Paul]

I dont' believe any F-26 ever came with a 454. My guess on the vibration is that the 1" shaft size is not big enough for a 454. (330hp?) This shaft will bow under the torque applied by the big block engine and a 19P prop which will cause a vibration. I would recomend talking to a marine machine shop that turns shafts. They would know what Ø is required for this length of shaft / horsepower.

[randyp]

My 77 F-26 HT has the stock Chysler 318 (225 hp) and the Mercuiser 233hp was the only option offered on my original spec sheet. I agree that the original prop would have not been sized correctly for this large increase in hp and most likely torque. If any part of the propulsion system is out of whack the vibrations from that much hp are definitely going to be felt. The fact that you can't get to WOT also points to a mismatched prop.

[foofer b]

RANDYP AND PAUL , ARE BOTH PROBABLY CORRECT, THE NEW ENGINE (~360HP) IS TOO MUCH FOR THE SHAFT AND PROP. THE VIBRATION REMINDS ME OF MY FATHERS 1968, 38' OWENS TWIN ENGINE, FLUSH DECK MAHOGANY CRUISER, THAT HE INSISTED NEEDED ANOTHER STRUT ON EACH SIDE. i THINK ANY MORE PROP WOULD BE TOO MUCH POWER FOR TH REST OF THE RUNNING GEAR AND SO FEEL RESIGNED TO STAYING AT 3000-3400 MAX RPM. ANY OTHER THOUGHTS OUT THERE?

[foofer b]

HOW DOES ONE POST THEIR BOAT PIC WITH THEIR RESPONSES?