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Old 01-12-2014, 06:51 AM   #1
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Re-powering Bertram 42

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?
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Old 01-12-2014, 07:37 AM   #2
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Might help folks answer if you say which model Bertram.

I'd have thought that would more likely be a planing hull, not even semi-displacement. Just a guess, though...

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Old 01-12-2014, 08:44 AM   #3
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He did. Vessel name, vessel model ... you might be familiar with it.
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Old 01-12-2014, 08:57 AM   #4
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Andrew, two questions, assuming vessel is in UK:

What brand and model are the current engines?
If you repower are the current Euro regs restrictive as to emissions?

On boatdiesel.com there are several UK members that could offer some help also.
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Old 01-12-2014, 08:59 AM   #5
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Greetings,
Welcome aboard. Something tells me even 220 HP engines would be to much. I vaguely recall some sort of "ideal" for what a vessel needs to achieve certain speeds. Something like 3HP per ton or 20 HP per gallon of fuel????? Can't remember at all but I'm sure some of the younger folk can enlighten you.
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Old 01-12-2014, 09:10 AM   #6
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Greetings,
Welcome aboard. Something tells me even 220 HP engines would be to much. I vaguely recall some sort of "ideal" for what a vessel needs to achieve certain speeds. Something like 3HP per ton or 20 HP per gallon of fuel????? Can't remember at all but I'm sure some of the younger folk can enlighten you.
RTF - my guess is the 220 HP was suggested by Andrew because it matches the ubiquitous Cummins 6 cylinder reman that is cheap, simple, reliable and available. Just a guess though.
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Old 01-12-2014, 09:42 AM   #7
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Andrew, the first thing you will need to do is determine if 20 tons is an actual weight or is the size area of the boat. Boats of this size in the USA are often listed in tons which is area and pounds which is displacement, not sure about the UK. My gut feeling is that 40,000 pounds for a 42' planning hull seams high.

While I think the Cummins 6BT 220s would work, one needs to understand that planning hulls are fuel efficient in displacement (7 to 8 knotts for a 42'), and somewhat efficient on plane (say 14 knotts for this boat), they may be really inefficient between 9 and 13 knotts. Basically most planning hulls start to push a big bow wave when they exceed hull speed and before they attain planning speed. Takes a lot of energy (fuel) to make a big bow wave.

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Old 01-12-2014, 10:45 AM   #8
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My first thought was that you'd ruin the resale value of the boat. My guess is that there are very few people who would want a Bertram that underpowered. Bertram's are built to go fast in rough water. If you were in the US I'd tell you to consider selling the Bertram and get a boat like OC Diver or mine which are designed to travel the in the speed range you're interested in.
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Old 01-12-2014, 11:11 AM   #9
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Greetings,
Mr. H. I would think a re-power of any vessel to a performance level not similar to original would impact on resale for sure BUT if the OP already has the vessel and is not terribly concerned about resale, the engine choices are pretty well limitless.
One could even go so far as to suggest running one engine and driving the two props. I think there are transmissions/drive trains that would allow this.
My initial comment was directed to what is the minimum HP necessary to achieve the desired results (12 knots max.) and I still think twin 220 HP is too much.
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Old 01-12-2014, 11:51 AM   #10
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One could even go so far as to suggest running one engine and driving the two props. I think there are transmissions/drive trains that would allow this.
The boat across the dock from us did exactly that..........
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Old 01-12-2014, 12:13 PM   #11
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The boat across the dock from us did exactly that..........
Is that called the Geared Up system. Philbrooks has been pushing this for a few years. BTW, nice clean install, but where is the exhaust run, RW feed line, fuel lines etc?
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Old 01-12-2014, 12:18 PM   #12
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While I think the Cummins 6BT 220s would work, one needs to understand that planning hulls are fuel efficient in displacement (7 to 8 knotts for a 42'), and somewhat efficient on plane (say 14 knotts for this boat), they may be really inefficient between 9 and 13 knotts. Basically most planning hulls start to push a big bow wave when they exceed hull speed and before they attain planning speed. Takes a lot of energy (fuel) to make a big bow wave.
Just to expand on this ... using the standard 1.34 factor, the displacement hull speed for 42' boat with LWL of 40' (just a guess) is approx. 9.5 knots. Anything more and the hull is being pushed up and over own bow wake and wastes a lot of fuel until it goes on plane (if capable).

Plan for that boat to cruise efficiently up to 9.0-9.5 knots.
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Old 01-12-2014, 12:25 PM   #13
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Just to expand on this ... using the standard 1.34 factor, the displacement hull speed for 42' boat with LWL of 40' (just a guess) is approx. 9.5 knots.
I get 8.5 knots @1.34 and using a more efficient 1.2 multiplier about 7.5 knots.
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Old 01-12-2014, 12:29 PM   #14
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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.
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Old 01-12-2014, 12:39 PM   #15
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Ted, hit the nail on the head with my concerns
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Old 01-12-2014, 12:41 PM   #16
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Is that called the Geared Up system. Philbrooks has been pushing this for a few years. BTW, nice clean install, but where is the exhaust run, RW feed line, fuel lines etc?
Yes it is the Geared Up System, the photos are just of the base mechanical installation done at Philbrooks.
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Old 01-12-2014, 12:44 PM   #17
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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.
My pocket express cruiser with modified-V planing hull and LWL of around 25' cruises efficiently up to 7 knots (exactly as the formula says).

The hull does not track well in the displacement mode as it is a modified-V hull ... or ... a modified flat bottom hull ... pick your poison ...
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Old 01-12-2014, 01:30 PM   #18
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I thought the idea behind a sport fisherman was to go like hell to the fish, spend the time fishing, not travelling, catch some fish and then zoom back to the marina to display the corpses? Isn't travelling at trawler speed a contradiction for a fishing charter?
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Old 01-12-2014, 01:31 PM   #19
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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.
not many people who charter a boat don't want a slow one they want to get there to fish,not spend all day getting ther
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Old 01-12-2014, 02:23 PM   #20
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The OP wrote: " 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."

That is the bottom line and if anyone can help him obtain that objective I am sure he will be happy and glad TF could help. I can't find any request for opinions on if the idea is "good" or not.

A string of folks telling him what he wants is not what they want or would do is no help to anyone.
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