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Old 01-12-2014, 05:26 PM   #21
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well it probably depends on how far your fishing grounds are! in Madeira Portugal you start trolling as soon as you leave port. the bertram is a great fishing platform at trolling speed in a lumpy sea ,so why not. most big game fisherman are catch and release there big fish now and thats how it should be !
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Old 01-12-2014, 05:29 PM   #22
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well it probably depends on how far your fishing grounds are! in Madeira Portugal you start trolling as soon as you leave port. the bertram is a great fishing platform at trolling speed in a lumpy sea ,so why not. most big game fisherman are catch and release there big fish now and thats how it should be !
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Old 01-13-2014, 07:46 AM   #23
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He did. Vessel name, vessel model ... you might be familiar with it.

Ah! Sorry, you're right.

I saw the 42, but on my screen, the "c" is wrapped way to the left on the next line, and I didn't see it.

You'd have thought I might have noticed that!

Definitely a planing hull. (I notice the spell-checkers always think that should be "planning.")

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Old 01-13-2014, 07:58 AM   #24
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thanks for all the reply's,
the boat is 1986 Bertram 42c sport fisher.
info i have is 20 ton actual weight and 39,400 lbs displacement.
existing engines are detroits 6v92 tas @430hp,
re powering with big like this size is,nt an option due cost.not worried about resale just cheap reliable running cost at that trolling speed.and enough power in a rough sea!
want it to take Madeira and set up a big game fishing charter.
i know this boat was designed for high speeds cruising at 18 knot and top 30 knots.

My concern is because the hull starts deep v then goes th shallow, with a planning chins that goes down it length,with low power would be fighting to push the vessel up ! and have a strange effect on performance. if it full displacement it would be easier to work out.

Andrew, maybe some useful data I can supply.

Our boat -- similar to yours, although lighter: planing hull, 35 gross tons (volume), and about 28,500-lbs displacement -- was manufactured with Cummins 370Bs, 450Cs, and Volvo 480s. Maybe some Yanmar 480s; not sure. Might actually have been a very (very) few with gas engines, no further info on that.

I spoke with an owner who had 370Bs and he was guite satisfied with performance. I didn't ride on that boat, but he sounded like he had a clue. He described cruising speeds lower than ours, I think in the 18-19 kt range. I don't remember what he said about tops speeds. (Our cruise with 450Cs is usually somewhere between 19-21 kts; we usually run at around 7 kts, though. )

Don't know what a 370B, perhaps reman, might cost, but I understand they're readily available.

Not a recommendation, just an observation.

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Old 01-13-2014, 08:08 AM   #25
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Will we be seeing the first Bertram with paravanes?
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Old 01-13-2014, 11:53 AM   #26
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Hi to all, i would be most grateful for your advice. this boat has twin 430hp,which are dead. i,m trying to redesign the engine size to my particular needs. all i want do is 8 to 12knots for trolling and be fuel efficient at that speed. would this be possible with this hull as its a semi displacement not displacement, i need know this achievable first. this boat is 20 tons and come on the plan at 14knots with the 430,s. but i dont need that it to plan, is this possible to re -power with say 220 hp engines?
One of things you might want to consider is that your 692's though heavy contribute considerably to the ballast and seakindliness of your boat. I have a 38 blackfin convertible, probably 10" less on beam and 10" more on draft than your hull. Fully loaded fuel water ice etc we are looking at 26 tons. We have the same engines but mine are j&t modified to 550hp and I have no tower. When trolling in big seas, the boat can be brutal at times. Not as bad if your amidships on the cockpit deck which is about 6" off the water but driving from the flybridge be prepared to brace yourself. At 12 knots it's manageable and on plane a whole different story, but I can't get her there on one engine. Two 250's maybe, if they were much lighter, but then I'd loose my ballast. The new berties have gone to much less vee and are now using gyro stabilizers for slow speed work.

In 1985 I was anchored in Funchal, waiting out a force 8 blow that seemed to come up out of nowhere. Nothing to do but windsurf all day in the rollers entering the harbor mouth. Definitely wouldn't want to be trolling at displacement speeds in those conditions. Most of the commercial fishing boats I saw were old school wooden portugeuse dories. Yes and there were a couple of Bertrams. Could have been your boat. Anyway the reason these boats go long on power is for the sport of bill fishing. Power is not always about speed, it's often about having agility when backing down in rough seas. My cockpit is 12x10x2.5 feet and I remember very well the first time it started to fill with water. Glad to carry 1100 ponies just for those occasions.

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Old 01-13-2014, 02:19 PM   #27
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Go register at boatdiesel.com and pay the membership fee. Then use their calculator to experiment with different engine sizes and see how fast each will make the boat go. What you get out of boatdiesel will repay the membership cost over and over again.
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Old 01-13-2014, 02:23 PM   #28
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thank you for a great reply, there,s alot to think about and alot i did,nt consider.
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Old 01-13-2014, 03:35 PM   #29
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You should be able to just run your boat now and take down the RPM and the speed, do this from 5 knots up to 10 knots. The RPM/HP curve for that engine (do a search for chart), those HP numbers will show you what you need at the minimium.
I think the Cummins 220hp reman'ed would fit the bill nicely, put in a nice gear and a tall ratio like 2.5: 1.
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Old 01-14-2014, 07:13 AM   #30
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His big problem is that 8-12K desirement.

At 8K the boat could cruise on very modest engines , although 7K would be markedly cheaper.

The hassle is it will require at least double the installed power for 12K , although with the surface area of the deep V it could be closer to triple.

The ride advantage in heavy water of the deep V is lost as a displacement boat , so only the extra drag is left.

SHOCK SHOCK !!! This boat might be better with a set of gasoline engines , as minor power does no long term harm and the need for big HP could be met as required.

Impractical as the entire engine room electricals would need replacing , and Im told gas is not dockside often in europe.

The easiest compromise might be a high out put diesel car engine.Yanmar or similar.

Small size so 30-40 HP each at slow cruise might not cost a fortune , and getting up on the plane would still be possible, for very limited time.


Lowest cost of all might simply be to overhaul , inframe the existing engines and set them up for a lower top HP output , just timing and injectors during the overhaul.

Resale would be maintained and saving $50K per engine package could pay for lots of diesel.
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Old 01-14-2014, 08:07 AM   #31
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Just curious - why no interest in rebuilding the existing engines? How far gone are they?
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Old 01-14-2014, 10:55 AM   #32
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Maybe this is of any use:
1) With a total length of 42 feet, the waterline will be more like 38 feet.
2) Not a big difference but the hull speed will be 6,16 x 1,34 = 8,25 knots.
3) Best efficiency / speed ratio 6,16 x 1,2 = 7,4 knots
4) If engines are swapped for lighter ones ( in weight ) you could consider to add ballast
which you could place actually lower in the bilge.

Calculation of power needed. This is total power at the 2 propellers and engines.
For 8,25 knots – prop.hp: 88 hp – engine hp: 94 hp total
For 9 knots – prop.hp: 103 hp – engine hp: 110 hp total
For 12,55 knots – prop.hp: 283 – engine hp: 300 hp total

Amazing that for the hull speed of 8,25 knots only 94 hp or 47 hp per engine is necessary. A safety margin for wind and waves add 100%, so the total power
is then (rounded off) 200 hp total or 100 hp per engine.

If you go this route you can choose for a (medium-) slow turning 1800 rpm
5 to 7 liter engine without turbo and aftercooler. The weight is about half of the weight of your GM engines and they last “forever”.

So far the calculations. Note that from 8 knots to 12 knots you need 3 times the horsepower, meaning you burn 3 times the fuel.

Personal experience: with my 22.000 kilo (loaded) catamaran with the sails down I always run 1 engine at the time. With a use of 3,25 liter per hour the speed is 5 knots.
For 6 knots it burns 4,6 liter per hour. (When I want to go faster I wait for good wind and I go 12 knots and do not need an engine at all, but that is not relevant here).
With the propellers 6 meters (!) apart I have to use 2 engines moving in marina’s and anchorages under 1,5 knots. Over that speed the rudders take over the steering and cruising they are slightly steering to one side to compensate the effect of the (one sided-) engine.

That practically all powerboats are overpowered makes interesting coffee-table talk.
( like talking anchors….)
An educating web-site is: Vicprop - Prop calculator for Displacement and semi-displacement hulls
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Old 01-18-2014, 03:19 PM   #33
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Andrew- a few options here: Since you do not have far to go to fish, fuel economy traveling is not a big deal. Rebuilding the 692's may be one option, and probably the lowest cost. Depends on what is wrong with them.

Another is to repower with small engines like the Cummins 6BT 220, or a similar Euro engine popular in your market. Cruising at hull speed around 8kts will not use much of the 220hp, but will load them enough to be happy.

Another is to repower with something like the Cummins 6CTA 450, which will allow the boat to scoot and preserves resale. This engine is more expensive than the 220, but you will gain that on resale.

The 450 will only burn a little more than the 220 at same speed. Guessing 0.5gph more, each.

That hull is not very efficient at low speed compared to one designed for slow.
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Old 01-18-2014, 03:52 PM   #34
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A string of folks telling him what he wants is not what they want or would do is no help to anyone.
Oh but Rick, the more information the better. You never know he might change his mind.

Powering to displacement speed makes sense, any thing more Unless you want to plane is senseless.

On my semi-displacement hull I avoid speeds just above displacement speeds, the speed just where the bow starts to rise. As Ted mentioned above you are just pushing water.

Perhaps the OP should go to a re-power specialist in his area and get some advise. I would be interested to hear what they say.
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Old 01-18-2014, 04:19 PM   #35
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Oh but Rick, the more information the better. You never know he might change his mind. Powering to displacement speed makes sense, any thing more Unless you want to plane is senseless. On my semi-displacement hull I avoid speeds just above displacement speeds, the speed just where the bow starts to rise. As Ted mentioned above you are just pushing water. Perhaps the OP should go to a re-power specialist in his area and get some advise. I would be interested to hear what they say.
A fishing boat needs to do ten knots in reverse. It also has to have sufficient power to safely maneuver with 12000 lbs of water sloshing around in the cockpit. Take a look at this and then decide if 200 hp is enough;

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Old 01-18-2014, 05:34 PM   #36
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A fishing boat needs to do ten knots in reverse. It also has to have sufficient power to safely maneuver with 12000 lbs of water sloshing around in the cockpit. Take a look at this and then decide if 200 hp is enough;

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A lot of pretty savy guys think that backing on a fish is just stupid and dangerous...there are other tactics proven effective to gain on a fish.

More than one owner/capt has sunk a boat , hurt crew or trashed an engine by backing down on a fish...not sure that I would ever do it to my boat.
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Old 01-18-2014, 05:37 PM   #37
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Resale isn't for everyone...some of us have factored in original cost, cost of improvements and maintenance...and see that in the long run if the boat is a giveaway/throwaway...so be it.

So someone that got a Bertram 42 for a song and want's to use rubber bands to power it for a few years then unload the hull to someone else or the dumpster...I can see the logic...actually someone might pay good money for the hull if the boat is in decent shape after another decade no matter what is done with the current engines.
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Old 02-27-2014, 07:40 AM   #38
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Imho....
I would never forgive anyone who would do that to a Bertram. I would sell it and buy what you want/need. It will never work well, as it was designed for a whole different purpose....and well designed they are.
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Old 02-27-2014, 08:40 AM   #39
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A lot of great information to chew on for the OP. I think the backing down vid is nice for tournaments where tagging and releasing quickly could be the difference between winning and loosing, but in reality lightly backing down and maneuverability is most important to keep your game out of the running gear.

So far the 450 Cummin's is the best advice I've heard so far.
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Old 02-27-2014, 10:37 AM   #40
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Why not rebuild

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Just curious - why no interest in rebuilding the existing engines? How far gone are they?
I would be willing to bet it would be far less expensive to rebuild these Detroits.
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