bertram31.com

I noticed that the large custom sportfish builders are making the exhaust exit through the bottom of the hull. Not only for noise but also for scavenging. Any one have any experience/comments on this? How much scavenging takes place from this? think its possible to have negative back pressure with t...

Looks like the 6lp gets better fuel economy than the 4lh at 30mph and about the same at 20mph. north of 2mpg at 30 mph seems "optimistic/optimized"... Can the cummins hit the same numbers in terms of fuel economy? Also, what's the deal with props. aside from loading the engines properly, what is the...

Do you think this was with stock shaft angles? 15* is stock right?

I saw this. are these numbers real? 2mpg with yanmars? 2.5 mpg with the 4lh? stock shaft angle? click the link to see the charts.

viewtopic.php?t=10102

Snipe and Ironworker,

What is your fuel burn rate (gph) at 30 knots?

I am curious to see the difference between 6bta and qsb.

So, We put new throttle shifters in the boat last night. Now both barbs are opening all the way. With 5.7 260hp (old), 1.5 ratios and 15" pitch props, the boat will hit 30 knots. I was pleasantly surprised...

Does any one run a Webasto Diesel heater? If so, how is it exhausted?

When you say 350s for power I assume you mean small blocks? If so, how does the boat run with the small blocks? It runs better than I thought. 260 HP 1.5 ratio trans with 15" pitch props. 3000 rpm gets us 21 knots for cruise. We are looking to up the hp on the small blocks when we rebuild (which we...

My boat has the raw water intake scoops. A friend of mine has a B31 with 440 Chryslers and his intake through hulls are not the scoop design, but simply a through hull hole (bronze) like it was for a though hull for a raw water toilet flush. no scoop. Any reason why the scoop design is needed? My bo...

What is a pair of velvet drives worth? Used c71 1.5 ratio. both working great.

Shoot-thru-hull transducers. What is every ones opinion for using it on a bertram 31? Any one tried it?

I see some radar domes mounted on the front on the fly bridge on B31's. With todays new radars, is this ok? Seems like the beam would shoot right through who ever is driving the boat on the bridge. I have a Bimini on my bridge. I would prefer no radar arch. Is the radar mounted on the front ok? what...

Here is why I ask. Currently have two freshwater cooled carbureted 5.7 sbc that counter rotate with velvet drives c71 1.5 ratios. My engines are on borrowed time. I really like gas engines because I can always make them run my self and do 95% of the work my self, which I really enjoy doing. with cou...

With counter rotating props... how important is it to have similar gear ratios? for example, one side would be 1.88 ratio and the other would be 2.1 ratio. Can this be solved with more pitch in the 2.1 ratio? Is there a problem with different pitch and different rpm props on a twin engine boat? What...

I have old gate valves for my raw water intakes. starboard side will not close. I know i need to replace both gate valves with ball valves. Any idea on how hard it is to remove (unscrew) the gate calves from the raw water scupper? any tricks?

Does positive rake, (angle aft) provide lift of the stern?

Lets talk about propeller rake. Can some one walk me though what it does? I see on outboards, alot of props have positive rake. With an inboard, in particular the B31, what is a good rake angle? pos or negative? and how does it affect the boat?

What does a 330 hp reman Cummins cost these days? Not installed, no gears. just the engine on a pallet.

Also, I currently have 260 gas. 1.5 gear ratio and 17D x 15P props with cup. 1&3/8 shafts. 1971 hull. oh and rudders that are the size of credits cards

So aside from thrust direction, less shaft angle also helps getting the hull out of the water when on plane?

Hey every one. What is the deal with shaft angle? I see a couple of people have really harped on changing shaft angle from the stock 15* to closer to 12*. Is it really worth it? Does it really make a difference in speed and efficiency? How about gas vs diesel in shaft angle? I know that the diesel w...