1971 FBC w/ Yanmars

[goombaysmash]

First and foremost, thank you for welcoming me to the board. I have been a longtime follower, but finally joined when I was approaching the ownership side!

I am currently on contract for a Bertram 31 that appears to be in very good shape; still pending engine survey next week.

Vessel History:

PORT ENGINE

- 2001 6LP-STE and rebuilt at 1950HRS due to replacement of STBD ENGINE

STBD ENGINE

- 2001 engine blew a piston and was replaced with a 2013 6LPA-STP2. PORT rebuilt at this time.

Current props are 20x23.

I was able to spec out the engines, but did not see the numbers that I expected (speed wise), but other than speed no other negative indication. This was an initial sea trial. We cruised at 22kts and at 3900 rpm 27.5KTS.

I spoke with Mastry and they informed me that I should, with specific props I should be cruising around 30 knots and WOT around 37kts. I am waiting on more data from Mastry, but I was wondering if the fact that these 2 engines have different HP ratings if that could cause such a difference?

Please note I am relatively new to diesel engines, but per manuals it appears that one is 300hp and the other is 315hp.

Thoughts/Comments are greatly appreciated and thanks in advance.

[scenarioL113]

What is your WOT RPM?

I think the engines are both rated the same


There are a few guys on here with Yanmars, if you can also let us know what your transmission ratio is?

[Tommy]

To Frank’s question, based on your props being 20 X 23, I’m thinking you have a 2:1 gear ratio. I had the 6LP-STE 315 HP, 2:1 gears and 20 X 23 props in my ‘73 Sportfisherman and cruised at 30 kts and top end at 34 kts.

[Yannis]

Yes, but whatever the ratio, 3900 rpm?
I think these 6lp’s are maxed at 3600.
A tad more than my 4lha’s that max at 3300.

[Carl]

Speed means nothing...sorta.

Motors need to make WOT...so need to know that spec.
If your not hitting that number at WOT, the boat is overpropped.
If your going beyond that number at WOT, the boat is underpropped.

If overpropped I'd expect to see a higher speed through the range and a shortened motor life. Black smoke.
If underpropped I'd expect to see lower speeds throughout...engines get to work easier. Some wasted hp.

Now if your turning the same 2:1 trans like Tommy had with those motors and the same wheels the boat "should" be running close to his numbers.

If that is the case what are some possible reasons:

Dirty bottom
Heavy boat
Wheels are out or not to the spec given.
Alignment, cutless, packing...
Running against tide or wind

Tachometers are not reading True (these should be photo checked...cheap and easy)



I'd start by verifying tachs and the ratio of trans...as the numbers provided seem off.

At the 22knot cruise, what was the motor rpm?


Speed validates everything is right and in order, provided the motors are not overloaded making WOT.

Have to get the balance of the puzzle to put pieces together

[Amberjack]

Amberjack runs Yanmar 6LP-STPs rated at 315 hp installed at Port Townsend in 2005.

1 3/4” shafts (I know, that’s substantial-didn’t want to snap a shaft launching off a wave. At least in those days).
20” dia props originally 17.5” pitch. More on pitch later.
ZF 1.5/1.0 gears
Currently cruising at 3400 rpms/ 28 knots
WOT I believe to be 3950 rpms but between watching for all the drift these waters have and the boat jittering in the chop it was only a quick glance.

The saga. We sea trialed the boat after installation and the numbers worked out fine if slightly over propped. I was new to diesels and relying on a decent mechanic during sea trials.

We originally cruised about 2500-2800 rpms (low 20 knots). The boat was getting a transom soot build up after 100 miles so my first step was to add 150 sq in air intake capacity per engine by installing Venus 150 ventilator grills low on the engine boxes in the companionway. This is a sweet solution and I have pictures if anyone is interested. The Yanmars need about 300 sq in each for fast cruising so the other 150 sq in comes from Capt Patrick’s “misc sources”. That reduced the soot a lot but it was still there so the props went in to have pitch reduced. I don’t have the new numbers with me here but WOT now is above 3900 rpms and the soot almost gone. Probably should have done the props first.

Mechanics and this forum said to run at higher rpms so now we’re cruising at 3300-3400 rpms and enjoying the rapidity. I give the transom a wash when I do the rest of the boat but that’s all.

[Bruce]

They are both the same hp. Engine blew cause nobody did the valve recall on those early engines.

If your using zf gears, they will be slightly different ratios because of the reverse rotation.

Those engines were recommended by Mastry to turn wot 3900.
Engine survey should have used photo tach cause dash tachs have been known to be off quite a bit.

Are you talking to either Doug or his brother over at Mastry? Cause 37 knots is a stretch.

[goombaysmash]

Amazing feedback from everyone! Thank you very much. The sea trial I did was preliminary to see if it was worth moving forward at a price point, but the surveys are scheduled for the 17th. This will include the photo tach to get an accurate reading. Per the maintenance records, maintenance performed by Shearwater in Stuart, the tach have been replaced and they informed me of the same. (BTW, I am new to these engines)

After hearing of the tach issues, I can lean that there may be an issue there, but that would result in both tach being equally off. I am not sure about that, but I could be wrong. The info I have gathered quickly on the board yields to me that a few systems need to be checked and aligned, but that it is attainable.

The engines are rated to 3800rpm and I brought them up to 3900rpm per a recommendation of a buddy of mine that was with me and had yanmar 315s. Remember this was preliminary for me to see if it was worth moving forward.

I am still waiting on getting gear ration and transmission model because the listing, per Doug at Mastry, stated that the information must be incorrect. The information on the listing that it. When I have this information I will report back to everyone.

The 22kt cruise was at about 3000-3100rpm. We were doing 27.5kts @ 3900.

@Amberjack, thank you for your info. Please send me pictures if you don't mind. The numbers you are reporting are in line with what I was thinking and have read with other 31 owners and our engines.

@Bruce, I spoke with Doug yesterday for about 45 minutes. He gave me that information. None the less he said my cruise, for the boat, should be in line with what @Amberjack was saying, if not slightly higher. Optimal speed is the result of many factors, but that this should be within reach.

Thank you for all your responses and continued support until I find the solution to reach the numbers I believe the boat is capable of. As @Carl stated earlier, there are many pieces to this puzzle that need to align. Unfortunately, the broker isn't very knowledgable on this vessel/engines so it has been a little difficult.

It is greatly appreciated and hopefully not a bother to anyone!

[goombaysmash]

I received the photos of the tags and boat is running 630A1-2.0R, so a 2:1 Ratio. Thoughts?

[Bruce]

Yes 2:1
But like i said, the ratio is slightly different for the reverse rotation engine.

Most 31 repowers using the 6LP used 2:1 gears because of the higher engine rpm.
I think I did 7 or 8 31's with the LP's and 2:1 gears.

I know some guys used 1.5:1 ratios, but you could still swing the proper prop for load with the 2:1.

Mastry was my Yanmar dist back when I was in the marine business, Doug and his brother Darrell(sales) are good people.

[goombaysmash]

Thank you @Bruce. I am waiting to hear from Mastry. Doug and Adib are looking into it for me. What numbers were you reaching when your repowers?

[Tommy]

Bruce did all the mechanicals on my repower; here are the facts:

1973 Bertram 31 Sportfisherman; Bimini Top; 220 gallons fuel; 2 people; moderate amount of gear on board; winds light and variable
Yanmar 6LPSTE 315 HP, Max rated RPM 3800; continuous cruise @ 3600 RPM; Preferred cruise 3000-3200 RPM
Hurth ZF Transmissions HSW63OA; Port 2.10:1, Stbd 2.04:1
20 X 23 bronze 4-blade props

RPM Knots
700 5.1 (idle)
2000 13.7
2400 19.0
2600 21.2
2800 22.9
3000 24.9
3200 26.7
3400 28.0
3600 29.6 (Maximum continuous operating RPM)
3800 31.5 (Maximum recommended RPM per Yanmar)
4000 33.0 (WOT; Bruce propped the boat to exceed 3800 when light so it would still hit 3800 under a full load)

[goombaysmash]

Thank you for the feedback @Tommy. The boat is very similar to yours and we tested with near-like conditions.

A few things I need to review as the listing has been off:
1) Confirm the props
2) WOT RPM

All indications lead me to believe the engines are healthy, but that there could be a prop issue. I was expecting to have similar performance as @Tommy, but that wasn't the case. I have yet to confirm the stamp on the props, but if they do happen to be 20x23 4 blade and the numbers I described are the yield and ultimately need to look into it further.

Thoughts?

Can't thank everyone enough here.

[Bruce]

Don't always rely on a prop stamp to tell you what size they are.

[goombaysmash]

Final piece of the mystery is that the props are 20x23 4-blade. I am going to have to wait until this is surveyed in about 2 weeks because I can't seem to see the cause at this moment. The cause of getting up to that speed previous mentioned and similar to @Tommy.

I am still planning to purchase the boat unless there is a major issue, but I am having trouble dialing this in. I believe it will be and will continue to update everyone.

Planning to fish it for the SoFlo sailfish circuit, last year I did it on my little Contender 23T. It was a great time for my green crew, but not looking for a beating again.

[THESALTYSATO]

I would like to ask if I am hurting or helping the longevity of my 6Lp's?

I have a 70 model Flybridge cruiser with Yanmar 315 HP 6lp's. I will put about 125 to 150 hours this year with about 75 % of those hours "cruising". I do not fish so I do not have a lot of idle time (which I assume would build up more carbon) because my wife and I like to take overnight trips with destinations of usually 3 to 4 runs each way. From my old Coast Guard days we we told to run the old 6 -71 diesels at 70 to 80% power. Because of that training, I have generally run my Yanmars at 28 to 2900 rpm's. At that rpm it is a comfortable run speed of about 25 to 27 mph depending on wind and current. Near the end of each trip I will run them up to 3400 to 3600 rpm's and sometimes open them up to 3850. Is this a good practice or bad? My fuel burn is generally about 10 gallons per hour total with the average GPS speed of about 20 mph because of no wake zones and boat traffic. I have ZF 2:1 transmissions, 1.5 inch shafts and my props are 19 X 22.775 LH and 19 x 22.768 RH and I service the engines every 100 hours.

[Tony Meola]

Hopefully one of the guys with these engines will jump in, but I thought I just read that you can cruise them at 3400 RPM's. If that is the case you have no problems but hopefully Bruce or I think Dug has Yanmars and will jump in.

[Amberjack]

I'm not on the boat but am pretty sure the engine data plate says 3800 max rpm/3600 continuous rpm. I've been happily cruising at 3300-3400 rpm which gives me 26-28 knots, plenty fast for these waters and it keeps the engine clean.

[Amberjack]

@Amberjack, thank you for your info. Please send me pictures if you don't mind. The numbers you are reporting are in line with what I was thinking and have read with other 31 owners and our engines.




No noticeable noise from the engines but Yanmars are quiet anyway. It seems counterintuitive to put air intakes down so low in the event we swamp the cockpit but once in the companionway water is going to wind up in the bilge anyway. I thought about it a long time, but in the end decided I preferred to have air intake holes inside the hull rather than outside the hull.

[goombaysmash]

Thank you for your comments. I had to push my survey for another week due to one of the technicians being diagnosed with Covid, but I am still highly considering buying it. I have an accept/reject date of October 6th, but I think I will pull the trigger before hand. I am eager to get started and working on her.

[goombaysmash]

Trying to get additional info on the vessel. My hull number is 556-601. Any thoughts or history on #s that someone can share?

[Bruce]

I would like to ask if I am hurting or helping the longevity of my 6Lp's?

I have a 70 model Flybridge cruiser with Yanmar 315 HP 6lp's. I will put about 125 to 150 hours this year with about 75 % of those hours "cruising". I do not fish so I do not have a lot of idle time (which I assume would build up more carbon) because my wife and I like to take overnight trips with destinations of usually 3 to 4 runs each way. From my old Coast Guard days we we told to run the old 6 -71 diesels at 70 to 80% power. Because of that training, I have generally run my Yanmars at 28 to 2900 rpm's. At that rpm it is a comfortable run speed of about 25 to 27 mph depending on wind and current. Near the end of each trip I will run them up to 3400 to 3600 rpm's and sometimes open them up to 3850. Is this a good practice or bad? My fuel burn is generally about 10 gallons per hour total with the average GPS speed of about 20 mph because of no wake zones and boat traffic. I have ZF 2:1 transmissions, 1.5 inch shafts and my props are 19 X 22.775 LH and 19 x 22.768 RH and I service the engines every 100 hours.

How your running the boat is just fine.

[THESALTYSATO]

Bruce and Tony thanks for the replies and information. I am new to diesels and did not want to jeopardize their longevity. They are great engines and to me are fuel sippers for the performance. They currently have just over 1,000 hours and do not burn any oil between oil changes--every 100 hours. Again thanks for the response. The forum is great for the info and is tremendously helpful.

[goombaysmash]

Survey Results!

This week, Wednesday and Thursday, I had the boat surveyed. The survey confirmed pretty much everything that I had seen, plus some items that were only noticeable out of the water. I wasn’t there for the Haulout/Launch as I was proving a point to a seller worked in my favor, but I have all the photo and video (I will also haulout/launch again as it was only a few hundred bucks).

1) Overall performance: increasing as at 3300 they did 25.5kts and at 3900 30.4kts. Props still need to be serviced as pressure cleaning didn’t take off all the growth and there are some hoses that are drawing water while running. Resulting in a lot of watch coming into the boat (replace all hoses is a must and I am not sure as to why the owner hasn’t done it.

2) Fuel tank will need to be replaced as the protective coating appears to be compromised in some fashion. There is water build up under the coating.

3) STBD Inside stringer needs to be replaced as it is delaminating and since I will be popping off the deck I will most likely replace all stringers.

4) There is a long list of miscellaneous items, but the majority are above and will allow the boat to be seafaring. Additional customizations are to come, but the idea is to get this boat seaworthy so that I can compete in the circuit starting December (I think I will miss the first one).

The engines are in very good condition and overall the boat is in good condition, but was fairly left alone for many years. Still working on the price point, but hoping to hear back tomorrow and if so i will close before the end of the week.

Thank you all in advance and looking forward to the help and recommendations in the coming weeks!

[Yannis]

Watch it, because Dug with 4LHA’s has very similar numbers, if not better. I do too, with 4LHA’s in a 28.

[Bruce]

If your sure rpm is correct, 3900 is where Yanmar told us dealers to run them wot.

Bertram stringers usually were roving over wood. Wood rotted out under most time.
Are you talking about engine support stringers? They should have been redone when repowered. Or are they using old gas stringers cut down with angle brackets?

Fuel tank aluminum I take it also?

[Rocky]

3) STBD Inside stringer needs to be replaced as it is delaminating and since I will be popping off the deck I will most likely replace all stringers.

Well, as I understand it the Bertram stringers are built so robustly (mine were over 3/8"thick) that even if all the core material rotted out inside you still have boxed in, high strength stringers integral to the hull. And some manufactures even have hollow stringers with limber holes built into them for drainage. So it was explained to me by Capt Pat, to not worry about the "core" inside them it was more in way of forming for the layup.