are these numbers real?

dognduck · Post by **dognduck** » Dec 29th, '23, 15:53

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

Amberjack · Post by **Amberjack** » Dec 29th, '23, 17:20

I’ve been getting 1.67 nmpg=1.92 mpg in full vacation mode i.e. groceries, ice, average 3/4 fuel tank so yes, I can see 2.0 mpg fully optimized. Can’t speak for the 4LH but I know people like them as an efficient, reliable engine.

Yannis · Post by **Yannis** » Dec 30th, '23, 00:14

My 28 with 4LHA’s burns 2,6 liters per nautical mile, all yearly miles and idling combined.
The miles (which miles?) per gallon notion is unknown to us.
Or, around 60-65 liters per hour at 24-25 nm cruising speed.

Carl · Post by **Carl** » Dec 30th, '23, 09:12

What jumps out at me is the 9600 pound boat weight.

My Express with gas motors, 162 gallon tank, and no water was 14000 pounds. I’d think if my boat went on a diet losing 4,400 pounds it would have much better performance numbers.

Yannis · Post by **Yannis** » Dec 30th, '23, 16:21

Carl, they may have erroneously taken the bare boat weight without the motors.

John F. · Post by **John F.** » Dec 30th, '23, 18:26

Awfully fast too

Amberjack · Post by **Amberjack** » Dec 30th, '23, 18:56

Are these numbers real? Well, Mastry is an engine dealer. I’m sure everything was optimized.

Carl · Post by **Carl** » Dec 31st, '23, 10:30

Yannis wrote: ↑Dec 30th, '23, 16:21 Carl, they may have erroneously taken the bare boat weight without the motors.

John F. wrote: ↑Dec 30th, '23, 18:26 Awfully fast too

Amberjack wrote: ↑Dec 30th, '23, 18:56 Are these numbers real? Well, Mastry is an engine dealer. I’m sure everything was optimized.

I believe dry boat weight advertised was around 10,500

Yes, faster and more efficient than the real life numbers I am aware of.

Doug hit on where I was going…the data sheets are not false but perhaps “optimized” numbers. It is the fast talking at the end of a car commercial where they say mileage may not reflect real life mileage. Thats because professional drivers drove on a closed course with rolling stops, limited breaking and lots of gliding at idle. My guess, stripped out super light boat and the 4 men are not 6’6 beer drinkers. Keeps the boat light, fast n efficient plus they reference mph over knots for a more satisfying number.

So is it real, yes, just not what most will see once some real life weight is added. Thinking back to when I purchased my boat…guy had cleaned it out, I still removed 6 big n heavy trash bags full of Chatch-key

dognduck · Post by **dognduck** » Dec 31st, '23, 10:59

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

Carl · Post by **Carl** » Dec 31st, '23, 12:37

Spec sheets are from 02, I don’t recall repowers looking to reduce shaft angle back then.
I’d bet stock 15°angle.
There was also a stock 10°angle setup in the early years. That was for gas motors with no reduction and small 15” wheels and 1-1/4” shafts.

Personally I think it’s advantageous to speed, economy,and handling but I’d love to see a real side by side comparison between stock and enhanced angle with all other variables the same. I’d guess at best it’s a few percentage points.

Tony Meola · Post by **Tony Meola** » Jan 2nd, '24, 22:39

Doesn't Dug have the 4LH in his boat?

Tony Meola · Post by **Tony Meola** » Jan 2nd, '24, 22:41

Carl

The pre 1973 boats were about 2000 lbs. heavier. My boat comes in at 12,000 lbs. with a full tank. That is after the installation of the diesels. I don't have a weight before, since the travel lift, I use to get hauled with did not have the scale on it.

Carl · Post by **Carl** » Jan 3rd, '24, 07:47

Tony, I knew the earlier boats were heavier, but didn't know when that changed and had no idea it was so much weight, it's literally a ton of weight. Thanks for the info.

Yannis · Post by **Yannis** » Jan 3rd, '24, 09:42

Tony,

Is that so only for the 31, or for all the Bertrams?
When I changed/inspected my through-hulls, I saw a 2cm thickness in the bottom. I consider this a "tank build"...mine is a November '72.
I wonder if you cut through a modern bubble boat of today, how much thickness there is in the bottom of their hull.

Tony Meola · Post by **Tony Meola** » Jan 3rd, '24, 21:37

Yannis

It was all of the Bertram's. Can't speak for other manufacturers. If you remember 73 was the oil embargo and the price of oil started to rise sharply. The bean counters got involved and to save money and keep cost of the boats down they thinned out the hulls to save some money. So yes, your boat went on a diet also.

Carl

Our friend had a 68 Fly Bridge with a lower station. There was a noticeable ride difference between his boat and ours. Later on, I found out the boats differed in weight. His boat came through with the 440 Chryslers.

Yannis · Post by **Yannis** » Jan 4th, '24, 01:39

Tony,

The oil embargo started in October 1973.
My boat was built in November 1972

Do you mean to say that they had already started saving on materials one year prior to the embargo?

Carl · Post by **Carl** » Jan 4th, '24, 07:48

Tony Meola wrote: ↑Jan 3rd, '24, 21:37
Carl

Our friend had a 68 Fly Bridge with a lower station. There was a noticeable ride difference between his boat and ours. Later on, I found out the boats differed in weight. His boat came through with the 440 Chryslers.

What did you notice as being different with the 68's ride Tony?

I think the strakes were changed somewhere in the early years as well. Cutting 2000lbs is substantial and they did that while making the gas tanks larger...interesting. And my boats deck is lower...I should change that as I'm not a fan of having scuppers so low.

Amberjack · Post by **Amberjack** » Jan 4th, '24, 15:23

Yannis wrote: ↑Dec 30th, '23, 00:14 My 28 with 4LHA’s burns 2,6 liters per nautical mile, all yearly miles and idling combined.

1.49 nmg

Yannis · Post by **Yannis** » Jan 4th, '24, 15:52

Thanks Doug!

Amberjack · Post by **Amberjack** » Jan 4th, '24, 17:56

Now you can communicate with us Amuricans

Yannis · Post by **Yannis** » Jan 4th, '24, 22:51

It is somehow a permanent issue because you have chosen to differ in every measure possible!
Even when you just say “dozens” of anything really, we say “tens” ! Anyway...

The 31 must be a little more economical than the 28. I think that Dug S. who runs 4LHA’s in his 31 has better figures than me.
Either faster for the same consumption or more economical for the same speed.
Is it the 60 or so centimeters of longer waterline? Who knows...
And now this 2.0 or even 2.5 mpg, these figures appear unattainable by any 28 I know of.
Either way, like we have all agreed in so many instances, the cost of fuel is not the most important outlay for our boats.
We are gallantly offered so many other opportunities to go broke lol !

Carl · Post by **Carl** » Jan 5th, '24, 09:39

Yannis wrote: ↑Jan 4th, '24, 22:51
The 31 must be a little more economical than the 28. I think that Dug S. who runs 4LHA’s in his 31 has better figures than me.

Either faster for the same consumption or more economical for the same speed.

And now this 2.0 or even 2.5 mpg, these figures appear unattainable by any 28 I know of.

Yannis...I'm glad you're starting to realize that the 31 is just a better boat. Some have even said it's The Best Boat Ever Made.

LOL, I was going to let your comments pass, but its a new year...

On a serious note, that is Interesting that your boat's performance numbers are lower. My dad does better with his 28' Hatteras than me...but the Hatteras is a flat bottom towards the stern, so his boat gets up and out of the water n goes even though his boat is much heavier. I could be wrong, but I think the 28 has more of a V going all the way back to the stern whereas the 31 does flatten out some with chines and strakes to add lift. I'm just guessing as it has been a long time since I was under a B-28.

Yannis · Post by **Yannis** » Jan 5th, '24, 14:02

Carl,

Happy new year to you and yours!

Thank you for your comments, I sense your sincere desire, to the point of jealousy perhaps, to hop on the model with the deepest vee in the Bertram family, as well as the best seller of all Bertram models ever!
So, the invitation is open; if you can't make your dream come true in the US, and can still tolerate a 10 hour flight (which I can't anymore), hop on a flight in the summer, preferably in July or September as August is too busy. This holds for everyone in the sandbox too!

I'm in deep crap with my boat currently, as on my way back from the islands in September I encountered Bertram weather and all my superstructure broke loose...I decided to not install the solar panels or the bimini, or fabricate a new stainless flybridge superstructure anymore, I'm in the market for new flexible panels that I will install on the forward leaning surface, as for the shade of the bimini I don't care much as from June onward I become so tanned and bodacious that even the sun fears to show around my boat, LOL !!

Earthquakes, planes on fire, wars all around, I hope 2024 will be better than the covid period but has surely started on the wrong foot...

Tony Meola · Post by **Tony Meola** » Jan 5th, '24, 22:12

Carl

You could feel she weighed more. She handled a head sea slightly better. He had the smaller fuel tank, but he added an additional tank to get up to 220 gallons. She ran at the same speed as ours, used the same amount of fuel, but she just had a slightly better ride. On a canyon run together, when we fueled up after the trip, we were within a gallon of each other.

We had the MerCruiser's, and he had the Chryslers. But I will say this, we raised more fish than he did. Trolling side by side we would raise 3 fish to his one. I put my money on one of two things, engine noise and our bottom stayed pretty clean and held the blue color since we docked in pretty clean water in a different area. His hull by August would be stained brown from the Cedar Water in Forked River.

Tony Meola · Post by **Tony Meola** » Jan 5th, '24, 22:13

Yannis

Don't let it go to your head, but I think the 28 is a better head sea boat, but it's that dam roll.

Yannis · Post by **Yannis** » Jan 5th, '24, 23:07

Yes, Tony, and this damn roll is the result of a super vee in a shorter boat...

Mind you though, that for us here who almost never use our boats for fishing, in other words, who are almost never static/idle in the middle of the sea, we are not really influenced by any roll! We are either cruising, or tied up in a marina, so very little exposure to waves or swell.
And if we are at anchor in a small bay, the wind/wave action always comes from the bow, by definition, so no roll there either.

ktm_2000 · Post by **ktm_2000** » Jan 6th, '24, 11:46

you all are crazy who's boat is better

The 25 is where it is at, with 300hp, I get an honest 25kt cruise at 2.8mpg

and to boot it rolls like all heck
https://photos.app.goo.gl/1XY5TTgzyGvbxWz98

DanielM · Post by **DanielM** » Jan 6th, '24, 15:00

Yannis,

I regard to the metric system. I used to work for a multinational chemical plant (Used to…that sounds funny to me. I retired 6 days ago after 39.5 years) and all my sister plants around the world were metric. On this side of the pond most every plant in the States used imperial units. Except mine in Texas, we used imperial units for pressure and centigrade for temperature. I never could figure that one out.

So sometimes even we can’t make up our mind... A nice Spring day to me is 72 deg F but my reactors ran at 280 deg C

Also I’ve been searching Craigslist for Bertrams for quite a while and last month I saw an ad titled “Bertram 28 – The best boat in the world ever!” somewhere in California. When I saw it I immediately thought “hmm, must be Yannis’s cousin”. lol

Good luck with your superstructure issues.

Geebert · Post by **Geebert** » Jan 6th, '24, 20:03

My boat is a 1969 sport fish, weighs 10,320lbs with mercruiser 454s and full tank of fuel. No water.
I think i could hit 9,600lbs with about 30 gallons of fuel. Boat only no people.

Tony Meola · Post by **Tony Meola** » Jan 6th, '24, 22:15

ktm_2000 wrote: ↑Jan 6th, '24, 11:46 you all are crazy who's boat is better

The 25 is where it is at, with 300hp, I get an honest 25kt cruise at 2.8mpg

and to boot it rolls like all heck
https://photos.app.goo.gl/1XY5TTgzyGvbxWz98

I think your roll problem is because your crew will not stand still. LOL

That is great.

Tony Meola · Post by **Tony Meola** » Jan 6th, '24, 22:17

DanielM wrote: ↑Jan 6th, '24, 15:00 Yannis,

I regard to the metric system. I used to work for a multinational chemical plant (Used to…that sounds funny to me. I retired 6 days ago after 39.5 years) and all my sister plants around the world were metric. On this side of the pond most every plant in the States used imperial units. Except mine in Texas, we used imperial units for pressure and centigrade for temperature. I never could figure that one out.

So sometimes even we can’t make up our mind... A nice Spring day to me is 72 deg F but my reactors ran at 280 deg C

Also I’ve been searching Craigslist for Bertrams for quite a while and last month I saw an ad titled “Bertram 28 – The best boat in the world ever!” somewhere in California. When I saw it I immediately thought “hmm, must be Yannis’s cousin”. lol

Good luck with your superstructure issues.

Danny

The best day of work was my last and my best day after retirement was that first Sunday night when I realized I didn't need to worry about Monday.

Yannis · Post by **Yannis** » Jan 6th, '24, 22:56

As they progressively appeared, Im still laughing with ktm’s despair that we’re quarreling in any manner! On the other hand, he’s got a point, don’t know how useful to us with real boats, but a point nonetheless.
Then comes Danny with his ever eloquent explanations, forgetting to admit that all these Fahreneits and non metrics are not used by anybody else on this planet. In what concerns what you read Danny about the 28, it’s simply true, only us are lo key and never show off like some others, haha!!!
The epitomy is Tonys comment on the moving crew...how true Tony indeed. It’s the price to pay if you want a bullet boat!!
It’s 6 in the morning, my friends left at 4, its my name day (St. John) and I produced a local havoc with food etc etc, I should be veering towards my bed ...happy new year boys!!

DanielM · Post by **DanielM** » Jan 6th, '24, 23:04

Tony I understand that feeling the first night you don’t HAVE to get up the next day. Mine was last Monday, I found myself laughing at the thought I won’t need to go in on Tuesday Jan 2nd.

It’s still feels kind of weird not going to the plant, but I’m not going to stop working. I like to fix up and sell an old house every couple years. But now that will be M-F days gig when I feel like it vs. having to pull evenings and weekends after the 40 hour a week job was done for the day.

That, and I have a mess of broken boats to fool with.

DanielM · Post by **DanielM** » Jan 6th, '24, 23:05

Dognduck sorry to derail. Hope you got the info you needed from the guys above.

DanielM · Post by **DanielM** » Jan 6th, '24, 23:19

Good night / Good Morning Yannis. Sounds like you had a good evening.

Carl · Post by **Carl** » Jan 7th, '24, 08:15

Danny- congratulations on your retirement!

Mathew- your kids enjoy a Little Rock with that roll! They do not seem to mind at all.

Yannis- Mother nature always wins, even Bertram weather takes its toll on our boats. Yes, we get back but screws n bolts loosen, if not secured it falls, and we find the weakest link in those times. Sorry to hear…sounds like you have a plan of simplicity moving forward. I am a fan of keeping it simple. And of course I only poke at the 28 cause it’s fun back and forth banter with you.

Geebert- 10,300 is kinda close to 10,500 without the bulkhead. I assume the we are using travel lift weights…I take those measurements with a grain of salt. In any case, kinda close. My express has bulkhead and glass work continues back further. It may account towards the extra weight.

Tony- you were lighter but ran same speed with same economy as the 440 boat. Great, another variable, the motors, were the 440,s more economical? I can see the extra weight being nice in a head sea, more through then up n over with some extra momentum. That’s nice, but also nice when running in light seas to be light n faster.

Metric System- which is better or worse? At this point I do not care, I just wish we’d pick one. Some parts we make are a combination so one set of measurements have to be converted along with their tolerances…a royal pain. Then don’t get me started with thread sizes that overlap between the two…5/16-18 and M8 x1.25 ugh…slightly worn and they can almost be interchangeable. Key word is almost. Ugh…I got me started.

Back on the OT, I think it goes back to Doug’s answer, the numbers are “Optimized”.

dognduck · Post by **dognduck** » Jan 7th, '24, 10:11

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 ideal prop to push a b31? it looks like the 19x19 (1.5 ratio) is just as good as a prop that is 22 or 23 (2:1) ratio pitch geared down.

My current props are 17 diameter with a calculated slip of around 12%. seems like bigger diameter (more leverage to turn the tips) and needed to load the diesel is some what of a waste.

I assume square props (18x18) are the most efficient, or gear down and be over square?

Geebert · Post by **Geebert** » Jan 7th, '24, 12:32

Something i noticed that illustrates the "optimized" theory,
If you look at the sheet with the 6lp, it has a "past power" section with 330 horse 454s similar gear ratio as the diesel.
The 18x18 prop at the cruise rpm of 3200 is shown as about 72% efficient.

Vs the diesel props 18x19, 89.4% efficient and 19x19, 90.8% efficient, at the same 3200rpm.

Either someone is playing games with numbers, or the gas boat needed new wheels, or the oysters scraped off the bottom, or the same diet the diesels went on, to get to 9600lbs

This doesn't disprove the new installation claims, but dose illustrate "optimized"

Tony Meola · Post by **Tony Meola** » Jan 7th, '24, 21:25

Todd

Yanmars and Cummis are like apples and Oranges. One spins up like a gas engine, the other lower RPMs with a completely different torque curve.

The Yanmars I believe will spin a smaller wheel due to the difference in the RPM's and Torque Curve. So, when the Cummins is spinning a 20- or 21-inch wheel the Yanmars might be turning a 19-inch wheel.

Not sure what Dug is running on his.

Remember once you go beyond a 21-inch prop you are pushing the size limit and could see some hull burn from the prop wash.

trace elements · Post by **trace elements** » Jan 9th, '24, 10:16

The problem I always encounter is when you look at the published fuel burn curves for these engines published by the manufacturers, they never correlate with the fuel burn that is reported. I get everyone wants their fuel burn to be optimistic.

Here is the link to yanamrs website with the 6lp specs and fuel burn curve: https://www.yanmar.com/media/global/com ... asheet.pdf

Carl · Post by **Carl** » Jan 9th, '24, 10:50

trace elements wrote: ↑Jan 9th, '24, 10:16 when you look at the published fuel burn curves for these engines published by the manufacturers, they never correlate with the fuel burn that is reported.

I think that has to do with the variables. If they are testing in a boat, what kind of boat, how is it loaded, what is the temperature, and what about the winds and sea conditions? What is the boat's sweet spot, what is it compared to yours?
I'd think motors would suck up different amounts of fuel cruising in a trawler compared to a sportfish or a stagecoach type. Is it a heavy Deep vee Bertram or a light flat Bayliner.
Props...same size n pitch can have differences between manufacturers on performance never mind are they to spec, close or tweaked by a reconditioning? Variables, lots of em so I tend to read with a grain of salt.
Look, even in our 31's my 62 is heavier with a different strake setup...would you want to compare that performance to a late 70's model?

trace elements · Post by **trace elements** » Jan 9th, '24, 15:31

Carl wrote: ↑Jan 9th, '24, 10:50 I think that has to do with the variables. If they are testing in a boat, what kind of boat, how is it loaded, what is the temperature, and what about the winds and sea conditions? What is the boat's sweet spot, what is it compared to yours?
I'd think motors would suck up different amounts of fuel cruising in a trawler compared to a sportfish or a stagecoach type. Is it a heavy Deep vee Bertram or a light flat Bayliner.
Props...same size n pitch can have differences between manufacturers on performance never mind are they to spec, close or tweaked by a reconditioning? Variables, lots of em so I tend to read with a grain of salt.
Look, even in our 31's my 62 is heavier with a different strake setup...would you want to compare that performance to a late 70's model?

Carl,

So long as the engine is propped and geared properly, to use all of the horsepower an engine generates at a given RPM, then the fuel burn should be pretty close, within 5% of the manufacturer's spec. Long story short, diesel efficiency is often wildly overstated. Look at the fuel burn for 330 6bta cummins, if you're using all the horsepower a 330 cummins produces at 2400 RPM, you are burning 10.6 GPH per engine. That means to be anywhere near 1.5 MPG, you would have to be doing 31.5 MPH at 2400 RPM. Nautical miles per gallon would be even higher. 31.5 knots at 2400 RPM, no way.

I would bet most, of the diesel powered 31s are closer to 1.3 NMPG than they would care to admit.

ktm_2000 · Post by **ktm_2000** » Jan 9th, '24, 15:53

to me the variable is engine load and what the engine can do for WOT based upon what it is pushing for a hull and what it has for a prop.

If one setup, the boat combo with prop, the engine can hit well above WOT PRM and is under propped vs another rig that the engine hits the same RPM and burns more fuel, when checked, can still hit WOT and thus is properly propped.

Carl · Post by **Carl** » Jan 9th, '24, 23:38

trace elements wrote: ↑Jan 9th, '24, 15:31 , if you're using all the horsepower a 330 cummins produces at 2400 RPM, you are burning 10.6 GPH per engine. That means to be anywhere near 1.5 MPG, .

Trace, time to add a variable, what happens when the motor is not using all the power available at 2400 rpm? My thought it is not burning the 10.6 gph and mileage changes.

trace elements · Post by **trace elements** » Jan 10th, '24, 12:45

Carl,

That is a good point, but if you are not using all, or most of, the available horsepower available at a certain RPM, (incorrectly or inefficiently propped), then that may reduce your fuel burn, however, it would also reduce your theoretical cruise speed for a given RPM. The most efficient point of operation is going to be using all of the available horsepower at a given RPM. Commercial ships, where efficiency is a matter of business, use variable pitch propellers in order to use all power developed by an engine at a given RPM. This should tell you that it is more advantageous to use all the power under the horsepower curve than to underprop and hope for fuel savings.

Given the fixed nature of recreational propellers and marine transmission gear ratios, it is tough to use all of the horsepower available at a given RPM, but that results in just as much lost speed as fuel savings.

Carl · Post by **Carl** » Jan 10th, '24, 14:25

I believe the most efficient is way down at displacement speed. If I'm not mistaken ships run at displacement speed unless Cruise or Defense Ships where fuel cost can take a back seat at times. I think if you look at a graph showing range as speed increases the slope heads down as speed goes up...aside from getting out of the hole, pushing water speed.
I do agree for a given amount of power there is a sweet spot where the best cruising speed and range are achieved.