Bertram33 User Forum

Last Sat I threw a blade off my port prop. They are/were 3 bladed bronze 20x18's with a light cup. Engines are 454's with 1100 hrs with good compression, trannies are BW with a 1.9:1 reduc. At full load (full fuel/water, 4 pob) with these props I was getting right around 4K at wot, good for 27-28 knots depending on conditions. I could cruise at 3K-3100rpms for 19-20 knots. These were actually my spare props that I had cut down last year. My regular props are 21x20 nibrals. The nibrals did not spin up to 4K when loaded. In fact they only spun up to 3650-3700 and speed tops out around 26-27. I figured I would screw around with the spares to get it just right before altering my nibrals. Now that the spares are toast, I am contemplating getting 4 bladed nibrals (20x16 with a med cup). I'm told that I an expect to lose some top end speed, but that my cruise should be slightly higher at the same 3K-3100rpms. However, I was also told that I should've lost some speed when I cut my spares down from 21x20 to 20x18. In fact the opposite was true. I gained a bit of top end speed. I really don't care about top end speed, I just wanted to make sure the engines were not being over loaded and would turn up to their rated rpms (4K-4400 rpms). I was very happy with the 20x18 3 bladed. Is anyone running 4 bladed on 454's and what are they getting for performance? Cruise speed/rpms, etc... Thanks, Doug L. 1986 33 Bertram FBC Queen Elizabeth

Doug, I have a 1989 with 454s and 4 blades. They must have done a couple of different configurations on transmissions and props over the years. I have 2.57:1 gears and have 24x24 4 blades. They turn up to 4400 RPM, and cruise 18kt at 3200 RPMs. The boat perfoms better in rough seas with these props. I have a set of 23x26 3 blades that cruise the same, but the engines will only turn about 3900 @ wot. Bit less control in rough seas. Other than the RPM difference @ wot, I can't see the benefit of all the money. Except the 4 blades are smoother as long as everything is perfectly aligned. E.W. Dugan

Thanks EW. What are you getting for topend speed with the 4 bladers? 1986 33 Bertram FBC Queen Elizabeth

Well I put the 4 bladers on the boat Friday night. So far, here's my take: 1. Slow speed handling is improved. At docking speed when I give some throttle to kick the bow or stern over there is no cavitation. These 4 bladers bite fast. 2. WOT with full fuel, half water and 5 pob was just about 4300 rpms good for 26 knots. My old WOT with the 20x18 3 blades was 28 knots and 4100 rpms, and 26 knots with the 21x20 3 blades at 3750 rpms. I'm getting the WOT rpm no problem so I know I'm not over-loading the engines. 3. Cruise with the 4 blades is 3150-3200 for 18-19 knots. The 3 blade 20x18's cruised at 3000 at the same speed. I took the boat from Salem, Ma down to Plymouth, MA on Sat to get the hardtop installed. It took me just under 2.5 hours. Although I am not sure exactly how much fuel I used, the gauge seemed to move pretty quickly. I'll make sure I fill up before I leave. I think I might add and inch of pitch to get the cruise rpms down some. Right now I think I'm too close to having the other 2 barrels kick in. 4. Overall the new props are really smooth. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth

Doug, Good deal. Sounds like you got the right combo. The secondarys' will kick in about 3400, so if you pitch it up a bit probably won't hurt anything. I don't think my boat has ever seen 28 kt. 18-19 is all I ever push it @ 3200, but I have a 1/2 tower, 2 kids, wife, dog, and dive gear, fishing gear, inflatable and 15hp engine, + beer ...everytime I go someplace. So it is almost totally loaded. I figure about 26K to the 28K it is rated if we are out a week or so. E.W. Dugan

Thanks Gene. 1986 33 Bertram FBC Queen Elizabeth

Doug, noticed Sunday that you were riding really bow-hi. Could those 4-blades be lifting up your bow by digging in your stern? If you use the tabs to bring the bow down, can you throttle back & maintain the same speed? Just wondering now that I'm home & on the puter for a change. Al 1978 33 FBC NITES OFF

Al, I was just getting on it when you saw me on Sunday. As far as I can tell, the running angle is no different with the 4 bladers. Somewhere between 18-19 knots the bow comes down with little or no tab. I have tried using the tabs, but it doesn't seem to make a difference. Also, when you saw me, I had a full load of 6 people, fuel, and beverages. Any thoughts on Newport yet? Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth

doug, what size and pitch 4 blades did you end up with and are you happy . you have the same gears and engine as me. Tim Stamm Photo Finish 1981 33' Bertram FBC

Tim, The 4 bladers are 20X16 with a med cup. I can't say that I'm thrilled with them, but added a half tower soon after I got the props. I'm considering altering my spare nibrals (21x20) down to 20x18 with a light cup. See my post under the port engine losing oil thread. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth

I am debating on if i should change my 21x20's to 21x18 or 20x18. Once i take an inch off the diameter it cant go back on,on the other hand it looks like you guys have already done the testing for me, and with my engines only turning 3500rpm they can probably use the help.I dont really want to pay twice to have my props done.But the one thing i dont want to happen is to lose speed. Tim Stamm Photo Finish 1981 33' Bertram FBC

Tim, I don't think you'll be disappointed. When I made the switch from 21x20 to 20x18, I actually picked up speed. Do you have either a full-enclosure or a hardtop? Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth

I am pulling the props monday so i will set them at 20x18 light cup.like i said i really dont know for sure what they are now, but i will have them measured before i tinker. I have a half tower with weblon top and in the process of adding a full enclosure Tim Stamm Photo Finish 1981 33' Bertram FBC

my boat is back in the water with fresh bottom paint new zincs and i put the gfo shaft packing in.My props were cut down from 21x20 no cup to 20x18 no cup. My rpm gain was 600 rpm from 3500 to 4100. the boat now jumps up on plane with ease and without the sound of the engine working real hard as it did with the other props.I did not have my gps on board so i did not get any speed info ,however it felt like there was no loss of speed. I am installing a flowscan 9000 system this week. if i can install it properly i will be happy to get fuel readings. Tim Stamm Photo Finish 1981 33' Bertram FBC

Tim, It sounds like you're not wasting any time with that boat. I just got my props back from Accutech , I dropped 2 inches of pitch which should work pretty good. My heads should be done in a couple weeks, so I can start putting the engines back together soon , if the weather doesn't get too cold for me to be out there. The flow-scans can be a bit confusing to install. If I can help at all , don't hesitate to ask. Frank Price