bertram31.com

I"m sure this has been discussed before but I missed it. How do I get my B31 to go slow enough to troll live bait at 2-3 knots? On one engine forward and the other in neutral, my boat will do 5 knots. I do it now by bumping in and out of gear which is not fun. Putting down the cav. plates has no effect. Do I drag at 5 gallon bucket?
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Christianity advice

Without gear information its not possible to determine whether you have the option for trolling valves on the gears.

Trolling valves make the gears slip. Some don't like them, others have used them for years without any gear problems.

If you have the Borg Warner inline velvet drives, then the answer is no.

Another option is to have a set of props with less pitch to use when live baiting. This will over rev the engine at wot and reduce speed, so you'll have to be careful.

Sea anchors work also. Don't use a 5 gallon bucket or anything with a solid bottom.

take old car tire and throw it over board

I don't know what you're pushing, but when we get into the HP/speed discussions, I try to make this point. The props you put on a high HP engine will get you high performance/speed, but usually at the price of low end performance. If slow trolling is part of your fishing regimen, you have to factor that in. There are some options. One is to keep your prop pitch low for docking and trolling, but cup your props so they perform better for you at the higher rpms. Trolling valves on your transmissions allow for slippage and thus allow you to slow troll...just remember not to suddenly rev up and take off before normalizing the transmissions. Also, if you can, set your idle as low as is feasable for your engines. My Cummins 6bt's will cruise at 21 kts, but can also troll on one engine at about 2.5 kts. You'll troll slower of course against the tide. Everything is a tradeoff in one way or another. Low rpm diesels do turn bigger props, the higer rpm diesels like the Yanmars probably do allow you to move slower at the bottom of the scale. Walter

My 28b idles too fast also-- I use sea anchors while trolling. On the front of the sea anchor I run a line that attaches to the spring line cleat-- and then let out enough line so the anchor is about 3 ft forward of the stern-- a line from the back of the anchor up to the gunnel keeps the anchor from swinging under.(I have mine secured around my downrigger base) I have been doing this for quite some time--100's of charters---the problem with this set up is in the sea anchor-- the off the shelf ones will not hold up---Buggy Bags---google them on the net are made super super tough and will not blow out like every other anchor I have used. I recommend one on each side-- size is a big?? call them and they will be able to help you-- Here is the big secret-- once you troll with a set up like this-- you will be amazed at how stable the boat is in a beam sea-- no more deep v snap back

Good Luck Capt Dana

Walter... I have 6Bts also, while I haven't played with the idle adjustment mine are now running at about 680-700 RPM.. do yours run slower than that? How "low can you go?"

Capt Dana... Good info.. thanks!

That's very good as 6bts start to rumble at lower speeds. The lowest I have ever gotten is 650. My norm is just like yours. Walter

My 6BTAs can idle down to 650 too, but like it better at 700. The port ZF IRM 220A rattles like hell out of gear below 800. As opposed to gas engines, the 6B Cummins don't lose any idle rpm in gear, AJ does 5.5 kts at idle, 3.5 on one engine, but we don't slow troll around here. As Walter and some of the other Faithful have pointed out, a B31 with dieselsMOVES when you put her in gear.....no hesitation, just a bump and she goes. I can back AJ in a slip 2 inches wider than her in a 25 kt crosswind with no sweat. Just like putting your truck in gear. Big props, big torque, deeeeeep V hull, big Patrick rudders, and the rest is history.

UV

I have repowered my 1976 31 and have the task of making the right choice for props. I don't want to make the choice twice. I have some three blade 18 19 's that came with the motors. My guess is they are a little small. So it's time to bust out another thousand.

Does anyone have the experience of having this power configuration and a prop combination they are happy with? I will be in the trolling and efficiency mode not inter island speed races. Also, it's Hawaii so the seas will be bumpy. Last I have a 1 1/2 inch shaft size and origional strut and strut angle.

Fish on fishermen

Capt'n J

Capt, if you have 1.5 gears try the 21x22 three blades (Michigan Dyna Jet Nibrals), no cup - its what I run on my 72 B31 FBC with Cummins 6BTA 250s and produces 24.5 kts at 2400 rpm for cruise and about 2650 rpm WOT.

UV

Vicroy,

I do have 1.5 gears and appreciate everthing except the Nibrals (thats $2000.00 :) .
I have a question on why three blade and not four? My impression is four would be smoother and more efficient but I get a lot of third party information that may not be in my best interest.

Capt'n J

Just for comparison.. I have Bertram 33, not 31, FBC, weight is supposed to be about 22,500 lbs.. and Cummins 6Bs, 315 HP, and 1.5 to 1 trans.. I have 21d by 23p 3 blade no cup props.. seems to be the correct setup for me.. I can do about 25 knots at 2,600 rpm.. maybe 27 if I push it to 2,800 RPM, which I never do except for data. As others.. she wants to idle at 5-6 knots at 700 RPM.. I would like less speed at idle, but don't want to lose the top speed if the weather socks in and I want to get the family home.

Boats and marriages.. are always compromises!

Capt J - the advantage of the Nibral material for props is that it is a good bit lighter and stronger than bronze, so the blades can be made thinner, thus giving a little better performance. Is it worth the extra money? Who knows.......

The B31, even with Cummins diesels, is a very light boat, on the order of 13,000# loaded up. The three blade props give better top end, and the four blades better lower end. But since the 6BTA Cummins have such a huge amount of torque, my view remains that the added blade area of the 4 blades is simply not needed. The 4 blades have a good bit more frontal area and drag. My B31, fully loaded, will go from idle to WOT in about 7-8 seconds, so I'm sure not overpropped. As far as smoothness, after the Katrina diaster with mine, I have all new running gear and she's as smooth as silk. In any event, because the boat is so light, the 4 blades are probably a waste of money.

UV

you guys want to lower your trolling speed, just throw a line to me and you can tow the tubb. that should slow you down a bit.
Yea Charlie, I guess it's like a tire, only bigger

Vicroy,

Thanks for your reply and explanation of the three and four blade comparrison. I really like the logic and apprieciate the direction.

Mahalo,

Capt'n J

The only comment I will make on 4 blades is that when dealing with hp and gear combinations, you sometimes have to use 4 blades to be able to fit a wheel.

The current repower I'm doing is about a week away from splash and with the 260hp D4 Volvo's with 2:1 gears, a 20x24 DQX 4 blade was used.
A 3 blade would require too large of a diameter to fit under the hull.

I've run into this in other boat, engine, gear combinations also.

Nibral isn't really needed on a 31.

Bruce, that's a very good point, glad you brought it up - as usual. I have the oversized struts High Tide sells, and after I went to 1.91:1 gears I am running 22 x 24 3 blade Nibrals. I got a deal on them used and reconditioned, or I would have just bought bronze. These wheels fit, but are tight, and it taks some serious wiggling to get them on and off. My next set will be 4 blades, to try to ease this situation somewhat.