true 24-26 kt cruise

Fryedaddy · Post by **Fryedaddy** » Tue Oct 31, 2006 4:00 pm

I am about to repower my 73' 35b.myurrent set up is: cummins 6bta 300 hp, zf 220a 1.5 gears, 1.5 shafts, 21x22 3 blade props. I run a honest 21-22 cruise @ 2450rpms and fully loaded boat. Wot is 26kts @ 2950 rpms. My question is what configuration is needed to run a true 24-26 kts fully loaded? A few other notes are: boat was at one time a gasser.(It doesn't have the bubbles in the engine room) I don't want to raise the floor. The gennie has been moved to in front of the engines. Any help will be appreacated. I have also posted on boat diesel.com Thank you John Frye

franklyprice · Post by **franklyprice** » Tue Oct 31, 2006 4:39 pm

John, Welcome to this site. I don't know much about B35's , since I have a 33 SF but I am interested in purchasing the engines that you're taking out.I've decided that a good pair of running takeouts , such as your's are what I need, even if they need an overhaul. Do you have a plan yet as to what you're going to do with them?

JohnD · Post by **JohnD** » Wed Nov 01, 2006 2:31 am

John, Welcome aboard!! I too have a B35, mines of 72 vintage with gas motors. Needless to say I've been beating this diesel thing to death. You may actually be able to get the cruise you want out of your current motors by changing tranny's and props. In researching the issue for myself I've learned that for the B35 with Cummins 300/330 using a tranny with 1:75-1 ratio and cupped blades should cruise around 25kts or close to it. But if your motor's are tired and new is better for you then here are some of my thoughts: IMHO, you've got 2 mfg options Yanmar and Cummins, The CATs are just a little big and heavy for the same rating and without the bubble on the bottom there's not much room. As for Cummins, unless you run real heavy the mechanical 370 should just about do it with a 1.75 to 1 gear. I made my annual stop at the Annapolis boat show and spoke with Wes who owns an 80's B35 with the Cummins 370's and he's right at your cruise range. I can e-mail his contact info if you'd like. Otherwise the new electronic motors up to 425 would do the trick. As for Yanmar, The 370 or 440 should do the trick, but I'm not sure of gear or other details. I lean toward Cummins mechanical since there less $$ and a simpler design, as well as, being proven and good availability of manint shops. Also, their reman program allows you to repower and save $5-10k per motor and still get a premium product. br, JohnD John D "Lady D" Bertram 35 Pasadena MD

jav · Post by **jav** » Wed Nov 01, 2006 4:29 am

John, as just a quick look, it would appear to me that 370b's would be somewhat marginal to get what your looking for. This is based on your current info. If your current WOT of 2950 produces 26 knots, than your boat requires your current engines full power (300 X 2) to run at that speed. Put another way, to cruise at 26 knots continous, you'll need to extract 300 hp continuous from each engine AND that HP has to come from a prop demand curve that still allows the engine to see WOT + 100-200 RPM. The 370B's are 355 HP engines and they make 300 HP as low as 2100 RPM so on its surface, this appears doable. The problem is that you couldn't prop the boat to pull that HP that low in the RPM range or you'd never make a reasonable WOT RPM. So looking at it another way, to extract 300 HP from this engine requires 15 GPH of fuel. Using a typical prop demand curve from Cummins, that would place the engine RPM at around 2700-2800 for a continuous 15 GPH... which allows no margin for error and is still higher than recommended for this engine. As John D suggested, all this is based upon your current efficienies and there may be some gains to be had by altering ratios and prop efficiencies... however, these gains tend to be marginal (under 10% in most cases) so I don't think you could make up enough efficeincy with your current setup to get you there. With 370B's however, it might be possible.

CB35 · Post by **CB35** » Wed Nov 01, 2006 5:06 am

John has got it right. You need around 370 HP to get to your speed requirement. The bubbles are on the bottom of the Cat powered boats to clear the 506 TD's that the factory used and to give a couple of inches under the Cat oil pan. Cat 3208 375 HP remans will also fit. There was one at the Rendezvous. I just don't know how 370HP 6BT's will hold up; and 425HP forgetaboutit. Those engines are only 359 cubic inches. That is a lot of HP for the cubes. I wonder if the 450C's will fit? Charlie

Post by **dougl33** » Wed Nov 01, 2006 5:27 am

Charlie, I don't know why, but I was always under the impression that your boat did not have the bubbles. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA [img]http://www.bertram33.com/photogallery/p ... sabeth.jpg[/img]

IRGuy · Post by **IRGuy** » Wed Nov 01, 2006 7:55 am

John... I read your post above several days ago but refrained from commenting because I am not familiar with the B35';s, having a 1983 FBC. You might have read on other threads what I have, but in case you haven't I have 1996 Cummins 315 HP 6Bs.. 1.5 to 1 Twin Disc trans, 1.5" dia shafts, and 21D x 23P props. I am getting what you want in your boat.. 23 knots at 2,400 RPM, which is what I will cruise at max.. the 315 HP 6Bs are rated for max 2,800 RPM and should not be run over 2,600 RPM if propped properly. During the seatrials we were able to get 2,920/2,930 RPMs WOT for a short time. Tony Athens of the Boatdiesel forum says if I can run them at 2,400 RPM they will be happy and last longer, so I do that. Buzz K, who has a B33 FBC "Buzz Off" with newer Cummins 6Bs, 330 HP version, and the same gears/wheels gets pretty much the same performance as I do. The differences between a B33 FBC and a B35 ?? are unknown to me. I assume my boat weighs about 22,500 lbs.. not sure what your boat weighs. I believe the Cummins 315 HP 6B and their 330 HP 6B are the same engine with perhaps some different bolt-on components.. I have the speed vs HP and torque curves for these engines, and the only difference is that the 330 HP version is rated at 3,000 RPM while the 315 HP version is rated at 2,800 RPM, meaning you would probably never see the extra 15 HP except in an emergency. I would think the 370 HP 6Bs would get you where you want to go with your boat. If you want to talk one on one drop me an email. I will be happy to talk with you. Frank B - IRGuy@aol.com "Phoenix" 1983 FBC Wilmington, NC

Sean B · Post by **Sean B** » Wed Nov 01, 2006 9:24 am

quote:Originally posted by IRGuy The differences between a B33 FBC and a B35 ?? are unknown to me. I've always thought that the B35 was basically a B33 FBC with a larger cockpit. I sure there are some minor interior differences but I think the cockpit is the major difference. There is a B35 in our marina but I haven't seen a 33 FBC anywhere except in Mass, people just don't have them around here. So I'm not too familiar with those, maybe there are other big differences. Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com [img]http://www.bertram33.com/photogallery/p ... d_Time.jpg[/img]

jav · Post by **jav** » Wed Nov 01, 2006 9:36 am

quote:Originally posted by Sean Burlingham quote:Originally posted by IRGuy The differences between a B33 FBC and a B35 ?? are unknown to me. I've always thought that the B35 was basically a B33 FBC with a larger cockpit. I sure there are some minor interior differences but I think the cockpit is the major difference. The hulls are slightly different in length and the B35 has a partial mini keel that I don't think is on 33. I believe both are Napier hulls with 17 deg deadrise and similar strake arrnagements.

Rick · Post by **Rick** » Wed Nov 01, 2006 9:38 am

Huge salon in the B35 with close to the same cockpit as my 33SF. But the biggest difference that I saw was the relatively small v-berth in the 35. Engine room is setup like the 33FBC, under the salon but bigger than you would expect from a 2 foot LOA difference. Rick Ticket 85 SF Falmouth, MA

Brian Davin · Post by **Brian Davin** » Wed Nov 01, 2006 10:57 am

The 35' does not have a bunk option like the 33' FBC if I recall correctly, thus more room for a bigger salon? Brian '90 Bertram 33' FBC Never Say Never Guilford, CT (Homeport) Kinnelon, NJ (Home)

jav · Post by **jav** » Wed Nov 01, 2006 11:14 am

Brian, the newer ones do have a single bunk to starboard in addition to the V berth...but no double.

Fryedaddy · Post by **Fryedaddy** » Wed Nov 01, 2006 11:17 am

First, I want to thank everyone for their reply. I have read posts here and on the 31 site for awhile. Seanile is my hero for what he has done with his 31. My boat is definitly a project boat. The engines now have a lot of blow-by. So much so that the Coast Guard would ticket me. Just about everything needs to be replaced. Second, seems that there are very few opinions that are the same. Always need to lean toward the consenses. I will look at getting the 370. I also thought about the 420 6ctas. Will they fit? I have seen a pair and they looked longer. I want this boat to be an all around fishing boat. Meaning that I will fish offshore and in shore (tuna and stripper) as the seasons change. I welcome all opionions. And will need the "Faithfuls" help from time to time. Boy am I glad for sites like this. John Frye

Post by **dougl33** » Wed Nov 01, 2006 11:28 am

The 35 has a deadrise of 19 degrees and has a beam of 13'3". As was previously mentioned, it also has a small keel. The bottom line is its a completely different platform than the 33 FBC. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA [img]http://www.bertram33.com/photogallery/p ... sabeth.jpg[/img]

Rick · Post by **Rick** » Thu Nov 02, 2006 6:12 am

John, I know another B35 owner who just installed Cummins 370's. They seem to be a great fit for the boat. Gives him the 24 knots you're looking for and there appears to be plenty of room left in the engine room. His was gas originally as well. He then put Cum 300's and just recently upgraded to the 370's. He wished he did it long ago. Good luck ! Rick Ticket 85 SF Falmouth, MA