I have a Betram 46.6 with a couple of Detroit Diesel 8v71 turbo and i just can reach 18knts at 2150rpm.(max rpm LOADED) ( MAX. RPM "empty" 2600) I have a 28x34 propellers. Is this propeller's size correct to develop a 22knts cruise speed or do i have to change these propellers? which one is the size recommended in this case?
Man, What are you loading her with, My second wife and her family? OK, real questions; How long have you owned her? Same performance since? Any history or logs from previous owners? I assume 3 blade wheels. Condition of bottom, tab position & bow angle? Color of exhaust thru-out rpm range and do you have fuel flow meters? Does both the engines reach these same rpms? Last engine survey or tach verification? Winning Florida lotto numbers for tomorrows drawing. ,rc
That's a lot of pitch - I think 28x32 is closer to spec. Perfect would get 2450 unloaded, 2350 loaded but I don't expect perfect from old boats. Your unloaded RPM is too high. Are you going off VDO tachs? If so you need to shoot the motors with a gun to confirm RPM. How heavy are you (tower?) and what's the condition of the motors - how much is left of the 435hp those 8V71's started out with. As far as cruising that old girl at 22 knots - I don't think that's realistic.
My 1973 46 foot bertram with full tuna tower cruises easily at 22 knots using Gori stainless 4 bladed props. I have 2 sets and would be willing to sell one pair. My boat has 2 inch shafts. Allison m20 gears. That would be with full fuel and water and Kohler 12.5 kw gen set.
Welcome to Yacht Forums. Maybe an ad in the sale/trade thread would bring better response. Lots of Bertram fans here. After near 20 years, recently moved off of our Bert MY. <----- Look forward to read of your Bertram projects and adventures.
If you already mentioned that, I missed it. How come? I hope that's not for health reasons, as it just happened to a boating mate of mine.
We just donated our pristine 1973 bertram sport fish, all remodeled because we tried all summer to sell it. After an offer of 10k i finally said thats it. No more stupid tire kickers trying to take me for a ride. Purchased it in 1987 and it served us well. Bittersweet but at 81 it was time. Great memories. Great boat. The spare props are in the basement. Seems a shame to scrap them
Do you still have the props? I’m wondering what size they are. I may be interested in the pair as well