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I’m looking at a 1972 Bertram 31 Sport Fisherman that was re-powered with 1989 Volvo Penta TAMDA41A engines. They now have 1800 hours. I’m concerned that something is wrong performance-wise. The seller reports that with a clean bottom it cruises at 3200 rpm running at 16 mph (his term, not mine) and consuming 15 gph. From what I’ve read from other owners, 16 mph is too low and 15 gph too high. Is anyone out there running Volvo 41’s? What numbers are you getting?

If I remember correct they are rated at only 200hp and depending on how they are propped that would be close to the 15 16 knott speed that hp produces.

The fuel burn should be for both engines.

Thanks Bruce
Yes, you’re right, they are rated at 197 hp. The seller said 16 mph, which would be only 13.9 kts. Maybe he meant to say kts, but if the boat is doing only 16 kts, then 15 gph seems even more out of line. Doesn’t anyone out there have 41’s or know someone with 41’s and could tell me the fuel burn rate?

I do not have Volvo's but...

Installing 5.9Cummins BT's at 210hp per side. From my homework I expect to cruise 20knts at 23-2400 rpm burning 14-15 gph.
These motors are about the same weight at 1100lbs and turn up to 2600 WOT.

From other lower hp installs I found

4-53's the ol 2 stroke DD- I believe are heavier with only 140-150hp pushing the boats to 14 knts

Perkin's 185 hp motors give a 15-16 knt cruise



Does sound a bit slow and thirsty...but could be heavy or propped wrong too.

very helpful. WOT is 3800-3900, correct? If she won’t spin that high then she’s over propped (if bottom is clean and 2/3 full of fuel, and not overloaded with people and gear)?

I do not know specifics of your motors, so kinda guessing here...

But if your saying the motors are supposed to spin up to 3800-3900 I believe you can run motors 200 off the pins..so at 3200 you should have a good amount of push left. Could also explain the bad consumption as your pushing lots of water at 16 mph.

Of course you have to be able to hit the rated WOT or better.

Unfortunately with lowere hp we need to run closer to the pins to get moving.

I looked at a boat powered with Volvo kad42s which are 230hp I believe and the owner claimed 17kt cruise. So sounds about right.

You should be paying the price of a gas motor and no more for those motors. Most folks don’t like the reliability or the availability and price of parts.

+1 from here, where parts is a lesser issue.
Notoriously unreliable, rather too sensitive, too many things to go wrong.
In their I/O versions, forget it.

I second the high cost of parts. Looked at repowering my boat with Volvo's years ago and parts cost scared me off. If I remember right, a starting motor was $700...

Update: Sea trial last Friday. The former owner didn’t actually know the boat’s performance numbers too well. It turns out that she does 17 kts at 3200 rpm and 25 kts at WOT. Bottom was clean and fuel tank full. These are far better numbers and I was very pleased and bought the boat. Sailed her about 300 nm from Tarpon Springs (North of Tampa Bay), Florida, to the Palm Beach Inlet by way of Lake Okeechobee. When we hit the Atlantic at the St Lucie Inlet, there were 3 foot seas, winds SE, and we ran south at 17 knots for 40 miles. Now that’s excitement. Thanks to everyone for the thoughts. Next step, replace these baby rudders.

Eat of luck with her

Good luck with her. Enjoy the new boat.

3200 at 17 knots with ability to hit 3800-3900, I'd be happy with those numbers too!

So 3200 would be a slow cruise, and at that going 17knots gets you where you need to go at a good pace, while being stingy on fuel.

Reliability...300nm maiden voyage answers that.


Funny as sellers usually Overrate performance numbers to the buyers. Did he tell you it was an old wet running boat that couldn't handle sea's too?
Wonder if his wife was making him sell it...


Best of luck with her!

Another update: I’ve got her in the yard at Seminole Marine in Palm Beach Gardens; FL. Bigger rudders and new port shaft by Bobby Soles (shaft damaged from mis-alignment, Yacht Tech says), all seacocks serviced or replaced, bottom soda blasted, chips and blisters filled and hard painted, raw water hoses and stuffing box hoses replaced, props (3 blade18x19) polished, balanced and pitched up to 20.5 by Bobby Soles, new cutlass bearings. She’ll be out by this weekend, I hope. Eager to report her new performance soon. If all goes well I’ll be in the Bahamas by April.

Good to hear. Keep us posted on your progress.

Took her out today for just an hour. The problem of Port engine overheating has been solved (new raw water hoses from hull strainers to raw water pumps and strainers sandblasted and painted). 27 kts at WOT with stbd tach reading 4200 and port reading 3600 (rated max is 3800, I think). Clean bottom, 150 gallons of fuel (75 ton lift said 14000 lbs). props are 3 blade cupped 18 x 20.5. I’m very pleased with the performance and will work on the tach mismatch next, and if she’s under propped, that too. Further updates on cruising speed, mileage, and such soon.

update: solved the mismatched engine speed problem. bought a handheld laser tach. it shows that the port tach is quite accurate but the starboard was off by almost 10%. so when stbd said 4200 rpms, its was actually 3780. So, now that i was unafraid to run the stbd at WOT, i got 3780 on port and 3960 on stbbd with 100 gals of fuel and water temperatures of 174 port and 171 stbd on milwaukee hand held temp gun, running 27 kts at WOT and at 3300 rpms got 23.5 kts and at 2700 rpms got 17 kts, running an 18x19.5 cupped 3 blade bronze prop and clean bottom. thanks to everyone for all the help. now, it’s off to the Bahamas for yellowfin

Calva,

Is your boat named Lady K? I've admired it as I've ridden by. My home is just up the waterway from Seminole.

No, she is the Gypsy Dorothy, sea foam green sides, berthed by peanut island

Those numbers are impressive for that hp motors. You should be very happy. 23+ knots @ 3300rpm.... (since you WOT @ 3950ish) That will get you from point A to point B at a decent clip.

Good luck!