Bertram33 User Forum

Tim, I think 20x18 with a very light cup would be a great set-up. You're like a mad scientist. Keep up the good work blazing the re-power trail for us. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA

Tim, I don't think Doug was being his usual mathmatically precise self. I think he really meant 19.8751 x 18.253 to get it really dialed in. By the way Tim, what's it costing you to haul every time you change props. In my situation the haulout cost would end up being as much as the props themselves. Of course as a percentage of the total project, this is just a drop in the bucket. Al 1978 33 FBC NITES OFF

Tim, I would get the RPMs to wherever crusader tells you. That way at cruise, you know you won't be overloading anything. And if you have any warranty issues, they can't use the RPMs against you. I think the mileage(VS GPH) differences you're seeing have more to do with hull dynamics than engine RPMs. The beauty of the fuel injection you have is that the engine fuel useage and power output should be pretty linear through most of the useable range. With the old carbs there's the added issue of when the secondaries open on the carbs and it changes everything. So where your engines will do you the most good will be where the boat planes off , somewhere around 20KTS and your burning somewhere around 28 to 30 GPH. Frank Price

al, i have a diver changing the props at a $100 a pop.they come right to my dock the day i call and takes all of 10 minutes. Doug why do you suggest a very light cup? my props now are 20x20x4 med cup and i need to drop 300rpms .so my guess of what the prop shop will suggest is a 20x18.5 medium cup. Frank, it seems like in all the tests i have done so far the best gallons per hour does not compute to the best miles to gallon.we will let doug do the math as far as coming up with the scientific ratios for that but as far as i can see, it really counts at the gas dock if you look more at mpg than gph.and what i have noticed so far is that i get a better mpg cruising at 23 knots than i do at 18 knots Tim Stamm Photo Finish 1981 33' Bertram FBC

Tim, I didn't realize the props already had a medium cup. Don't "they" say that 1 degree of cup is good for 100rpms? If that's true and your only getting 4350rpms from 20 degrees of pitch, then dropping 2 degrees will only get you to 4550rpms. Knocking out some of the med cup will probably get you the other 50-100rpms. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA

each inch of cup equals 100rpm a med. cup is 3 inches hence 300rpm gain by adding a med cup now pitch is 200 rpms per inch. i just talked to my prop guy and we came to the conclusion to take 1.5" of pitch out to make them 20x18.5 med cup that should put me around 4600rpm we had a discussion of him wanting to do 19" since my boat was fully loaded with full fuel 2 adults 2 kids 3/4 water ice chest blah blah blah. but as the conversation went we decided that even empty on fuel at 1800 pounds of fuel that is not even 10 percent of the 22k the boat weighs.so we decided that even totally empty the boat probably would not exceed the 4800 rpms and i probably wont catch enough fish to drop to 4400 rpms....does anyone have info on rpms on their boat fully loaded vs fully empty? also regaurding cup my prop guy said that the cup keeps more water on the blades all the time without the cup you have more air bubbles hitting the props than you do with no cup hence an increase of the efficiency of the blades....i know now i am really sounding anal but this is all fun to me . Tim Stamm Photo Finish 1981 33' Bertram FBC

one other thing ...my analog tachs are not equal the port reads 150rpm dif than the starboard so i am not getting exact rpm figures and my floscan tachs go weird when i hit 4k....but when i did my sea trial the photo tach was very close to my starboard tach so i will be close when i do my first engine service in a couple weeks i will try to have the mechanic test the wot with the digital tach.if i am between 4550-4650 i will be happy. Tim Stamm Photo Finish 1981 33' Bertram FBC

Tim, Exactly. I said the engine is linear, the hull is not. That's because the hull isn't fully planing until you get to 23 knots.My problem is that with carbs and less horsepower, I'm pushing my engines enough at 20plus KTs that the secondary barrels kick in and then my engines lose what efficiency they had. With your new setup you don't have that secondary issue, so your able to get over that "hump" and keep it there without opening up two tennis ball sized holes in your intake manifold, like mine, and your old setup.I've said for years that they should have made fuel injection mandatory back in the sixties. Just think how good it would be now if they had done that. On your prop issue, I don't know why you need any cup at all, do you think it would be worth asking the prop guys what would happen if you removed it? Probably good for at least a hundred RPM. Frank Price

OK just read your last two posts, disregard the cup comments. Frank

Frank, i have talked to michigan wheel and several prop shops and they all suggest for our type of boat to have a cup for more efficiency. Tim Stamm Photo Finish 1981 33' Bertram FBC

Tim, I just took my boat out for the first time this year, thought you'd like to hear the fuel consumption #'s. at 3000 RPM I'm going about 18 Knots@ 24 GPH at 3300 RPM -21Knots @30 GPH at 3550 RPM -23 -24 Knots @ about 40 GPH. Now the speed varies a bit around here because of the huge tides and the strong currents they cause, so at one point I was going 18 Knots burning only 20-22 GPH going with the tide. You can see that at 21 Knots or so , the carbs start to kick in the secondaries and it all goes bad. What my engines seem to like is about 3000 RPM. Unfortunately that RPM won't push the boat as fast as it would like to go. Still, I think the engine work and prop work have gained me a little efficiency and I didn't notice it "lugging down" when it went through waves , like it did before and the secondaries on the carbs seem a lot slower to open, which I had hoped. I'll give it more testing over the next few weeks and keep you posted. Frank Price

Wow Frank those numbers are great..you should be very happy..it must be the new slick floors........congrats on getting back in the water... Tim Stamm Photo Finish 1981 33' Bertram FBC

Frank, your numbers are very similar to mine, but without the FloScans yet, I don't really know what my consumption is. Those are going to have to be my next purchase for sure. David Sumich Bertram33.com Forum Administrator

Tim, Any idea when you'll get the re-pitched props? What are you going to do about your old 3 blades? Will you have the prop shop look at them to see if they can fix the vibration issue? Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA

Doug, the repitched 4 blade are going on tomorrow...i pick up the 3 blades tomorrow and they will go in the bilge and hopefully stay there...and your props are on the way home via ups.thanks again your props helped alot in the process so when you get your crusaders they will work perfect.... Tim Stamm Photo Finish 1981 33' Bertram FBC