Max Speed Question

[JohnV8r]

What is the conventional wisdom on maximum speed in a B31 before the shaft angle starts to create stability issues from pushing the bow down. I can't remember the speed where things get iffy and I can't remember whether it was chine walk that created the instability.

Thanks in advance.

[CaptPatrick]

John,

Nose diving is not a factor of speed, but of over powering while maintaing the stock 15º shaft angle...

The stock shaft angle is fine for diesel power up to about 330 hp. Above that power range a much larger wheel is needed to properly load the engine, developing much more torque. Gas configurations can probably go to around 400 hp because they don't develop the torque of diesel.

The "Grim Reaper", a B31 that was severely over powered with diesels & the stock 15º shaft angle, would nose dive at about 29 kts & never climb past 30 kts. (Bruce did sea trials on GR August of 2003.)

The hull speed, (maximum safe operationg speed), of the B31 is widely accepted as 35 kts, (40 mph), & most B31s powered at 315-330 hp, w/ 2:1 transmissions, & roughly 20x24 four blade wheels will top out between 32 - 35 kts, depending on which model & how the boat is loaded with gear, fluids, personnel.

Br,

Patrick

[JohnV8r]

Patrick,

Thank you for the response. I'm looking at repowering with the new Cummins QSB5.9's. When I responded regarding the objectives for my repower, my primary priority was identified as, "I want more range. Equal in importance to range is to have the quietest most odorless diesel I can have."

I got the following response: "QSB's 380's would really be a nice engine for the boat as you would have all the power you'd ever need plus be smoke free at any temp or vessel speed."

The QSB 5.9 has the same footprint from 230 hp to 480 hp. Horsepower options for the QSB 5.9 are 230, 305, 330, 355, 380, 425, 440, and 480.

I'm assuming then that based on your response my options end at 330 hp, unless I'm going to change the change the prop angle.

Can the prop angle/high torque from bigger wheels issue be successfully modified without adding prop pockets? Would a different gear ratio have an impact or is the bottom line that 380 hp is just too much engine.

Thanks again.

JohnV8r

[CaptPatrick]

Can the prop angle be successfully modified without adding prop pockets?

No.

Without pockets you'd have even less space to swing the proper wheels. That's the only reason anyone would add pockets.

Coupled with the added expense of unnecessarily big engines, custom struts, custom rudder assembly, & 1 3/4" shafts, you'd just be dumping money down the crapper to be able to say: "Gee whizz, lookit what I done, but can't justify..."

For any given engine block, a manufacturer can offer a wide variety of hp ranges. Think of it like this: All things equal other than hp, the block with the lowest hp rating is going to out live, by a long shot, the same block at the maximum hp rating.

Lower hp equates to better fuel economy, (to a point), & lower cost, (usually).

If I were making the decision, I'd opt for the 230 hp version. That would give you an honest cruise of around 24 - 26 kts & probably top out at just around 30 kt, assuming a 2:1 gear ratio. Most days you can't cruise at over 17 - 18 kts on the open ocean without beating up the boat, yourself, and anyone else aboard. The 305s would be the most I'd go...

QSB's 380's would really be a nice engine for the boat...

That person is trying to push someone into the biggest coupon he can clip & obviously knows little more about a 31 Bertram than it's got a pointy front end...

Br,

Patrick

[Bruce]

John,
I've repower'd the 31 with the QSB 330hp. They are not quiet engines as you might have been lead to believe.
They are also not smoke or odor free. No diesel is.
While they are not the mosquito sprayers older engines are, there is a certain amount of smoke.

Also the QSB series has the most computer boxes and wiring of any model I've seen up till now.

The 31 I installed them in already had pockets built into the boat and the performance was within 2 knots of what I get out of the 6LP installs.

Think of changing the shaft angle in two ways:

1. Shortening the strut which reduces prop diameter and thus usefulness on any real hp gain.

2. Drop the engines beds down some. But as you do like any fulcrum, the shaft piviots somewhere, again at the strut. As you drop the front, the back raises. How much you drop the front will determine the rear height clearance.

I've yet to be on a 31 with a severe nose over situation except the Grim Reaper. While that was over powered, and poorly at that, the nose over was from more a weight problem. You see the owner was a metal guy who had all the bulkheads, some cabinety made out of aluminum and had a hugh tower with the feet way out front. There was just too much nose weight to begin with.
It plowed the nose which acted as a rudder opposing any control from the regular rudders.

Where the speed problem comes into play is the lift the 31 dead rise gives the faster you go. It will lift the boat to a point where it chine walks creating a dangerous situation.
There are ways to combat this situation by why bother.
Thats what they make 34' Ventures, Jupiters and Contenders for.

No need to reinvent the wheel with the 31 although there are those that do.

According to your priorities, I would chose the 6LP Yanmar.

QSB 380 would not be the choice for your priorities and certainly the person you talked to clearly didn't comprehend your wishes.

[JohnV8r]

Patrick & Bruce,

Thank you so much for the feedback. I really, really appreciate it.

The last thing in the world that I want to do is turn my B31 into some Frankenstein-esque experiment.

Thanks for your perspective.

Sincerely,

JohnV8r

[bob lico]

i don`t know when and where it started but i would consider any person who takes a sawsall to the bottom of a 31 bertram a idiot.i have test drove 12 28' luhrs and upteen 30,32,36,and 41' with and without prop pockets unless your only motive is the shallow water factor prop pockets on a 31 for high speed is conterproductive.i could be wrong but then so is viper,fountain,outer limits,and in fact not one a.p.b.a. boat in the world has dumb pockets.as the water goes thru the pocket there is water turbulance causing air bubbles the props lose there "bite".every high proformane boat in the world try to get the props in clean water,look at the big center consoles notice the twin 300hp on brackets that puts the prop further back from the transom in cleaner water.i installed my engines almost on the floor at the rear engine mount ,my shaft angle is 12degrees with the engines pull back to the fuel tank.at 38.3 knots the 31 bert is riding on the two bottom strakes!with the 21"x27" experimental props what the hell would those dumb pockets do with the boat on the two bottom strakes? use your head walk around look at a fountain bottom i know they are #5drives but at top speed there are tuck in forming a negative angle yes!!!! similar to your bert. the key is to shift all weight possible to the rear.case in point i even have my capt chair on the rear overhang of the bridge the boat is on perfect plane at 38 and at 40knot it becomes hairy sitting on the bridge hit anything over 3' and you will fly off the bridge. btw take that dumb pocket into a nasty following sea like a inlet when you have no choice.when or if you get to the dock you could paint eyes on your bare ass and walk backwards you need it for destroying the best bottom boat in the world

[CaptPatrick]

Bob,

I'm not even going to check your figures, it's enough to just say: Damn Boy, I like your attitude!!

Br,

Patrick

[bob lico]

part of it comes from reading your post for 5 years or so .mainly it defies my imagination why any 31 bert owner think he smarter or a better designer then ray hunt.consider the fact all performance boat use the same strake design with the added 1'cut just aft of midships for added lift.and some with a 8"flat at the transom this definitly sacifices good ride for increase speed but this post is not about a 100mph v hull,just a man way ahead of his time.---amen

[IRGuy]

John...

Just to add some perspective to your question and the responses above.. there is a guy on the B33 forum who repowered with Yanmar 370's. B33s weigh about 22,000-23,000 lbs.. he has 2:1 gears, 4 blade Nibral 22x25 wheels. With a couple of people and medium loading he posted the following results from his latest sea trial.

3450rpm(WOT) = 32.4 knots
3300rpm(max rating) = 31.0 knots
3100rpm = 29.0 knots
3000rpm = 28.2 knots
2900rpm = 27.3 knots
2800rpm = 25.8 knots
2700rpm = 23.5 knots
2600rpm = 22.1 knots
2500rpm = 21.4 knots
2400rpm = 19.9 knots

Of course we are talking different boats, you have a slightly deeper v hull and less weight. My B33 with Cummins 10 year old (but only 500 hours) 6B's (rated 315 HP at 2,800 RPM), 1.5:1 trans, and 21x23 3 blade wheels will do just about 10 knots per 1,000 engine RPM with 2 POB and half fuel and medium load.

How often do you have conditions when you comfortably move your boat over 22-25 knots?

Just trying to give you something to compare to.

[Capt. Mike Holmes]

Bullet, a real sharp 31 in Freeport, Texas with full tower and big genset, just repowered with 370 hp common rail Cummins. I think he told me it tops out at 36 knots, said they made an overnight trip in flat water running 28 knots coming and going. Given that, this same owner admits he usually likes to keep it under 20 knots. As others said, that's wasting money on power you don't need and rarely use, not good for the engines, either. Most Cummins powered B31's will be using 1.5:1 gears, as they have more torque and turn lower rpms than a Yanmar. I have 1.91:1 gears in mine, because its a very heavy 1962 express. I'm probably getting 250 - 270 hp out of my 6BTA's now, turning 22x24 three blade Nibral props, some cup. I top out at 25 knots, cruise pretty easily at 20 - 22 knots. Although it would be nice to run faster sometimes (and the boat acts like it wants to, just getting "happy" at 25), this is all I need.

[Bruce]

Bob,

I don't think anyone starts out wanting to cut pockets in a 31 for speed only. Its a result of using 330hp lower speed diesels and up and being able to swing the props needed to take advantage of that hp.

The speed is the end result of the proper prop usage and still be able to maintain a few knot idle speed without the use of trolling gears.

Offshore power boats don't use pockets cause they all use stern or surface drive systems and thus are not needed for prop clearance. Besides they are almost all using high reving gas motors.

As diesels, ie Steyer become higher in rpm, you'll have those 36knot speeds due to the ability to use smaller props but spin them faster.

The 31's I've been on that have had pockets have been very stable at mid to upper 30 knot range. The pockets didn't affect stability at all.

And the ability to have an idle speed of a couple of knots but still attain the high speed made it very pleasant to shift in and out of gear and dock.

Where Pat and I and others come together is right now there are engine, gear combinations that will get you a couple knot idle speed, 34 knot top speed without the expense of installing prop pockets.

The big caveat being how many times can you maintain a 32k cruise on a 31 and be comfortable in doing so?
Thats more of an argument then the prop pockets themselves.

Small high output diesels weren't around when the 31 was designed. Who knows if they had been, Ray might just have used them in his 31 with pockets.

[JohnV8r]

IR,

With my 330 hp Mercruiser big blocks, I typically cruise at 2700 rpms (my secondaries kick in at 2850 rpms). Depending on tide, wind, and load, that usually gives me a 20-21 knot cruise.

I have an 11 nautical mile trip to get from my marina to the Golden Gate bridge. In the mornings, I could pretty much go as fast as I want across the SF Bay. I would like to be able to cruise at 24-26 knots across that stretch in the mornings.

In the afternoon, the SF Bay is often (but not always) more snotty than it is offshore and I typically am limited to 18-22 knots.

Offshore up here I typically cruise 18-21 knots. In the mornings when the wind is down (which is most mornings), I often wish I could kick it up a few knots but don't right now because my fuel burn is significantly different when I get on my secondaries.

Ironically, I had the opportunity yesterday to go down to the Cummins authorized dealer in the SF Bay area and listen to a pair of 230 hp QSB's that they had just installed in a 32' Hatteras. The rep from the Cummins distributor was there too. We didn't get to take the boat for a cruise, so I didn't get to hear the engine under load. However, having been on Emmit Yeazell's B31 with Yanmar 6LP's before and now having heard the QSB 230's, I think I understand Bruce's comments above a little better. My initial impression is that the Cummins QSB is louder at idle than the Yanmar 6LP. That may be more about the tone of the engine than actual decibels. I think the exhaust smoke/odor is about the same...at least at idle. I also think the Yanmars may have less vibration, but then again I was on an older Hatteras so that may not be a fair comparison.

The thing that did blow me away was the technology and information with the QSB's. I won't bore everyone by going through a brochure-like listing of all the features, but the two things that blew me away the most were these: First, the fuel burn/range information is amazing. The nautical mile range (not just the gallons per hour) numbers actually change as you change the engine rpms/load. So say you're cruising along at 22 knots and your range is "X", if you drop down to 20 knots, your new range shows up immediately. The range is calculated by tankage parameters that are input in the system and, if I understood this correctly, by information from the networked fuel tank sending unit.

The other thing that blew me away was how the Glendinning shifter controlled the electronic trolling valves. Trolling valves are pretty important up here because you troll for salmon at 1.5-3.5 knots. The electronic shifter has a "troll" button that automatically engages the trolling valves while limiting the rpms. Bottom line: you can't screw up and blow the clutch in the gears by forgetting to disengage the trolling valves. Gone are the days of putting a sock over the throttles to keep yourself from doing something stupid. Even more impressive, the gears are fully warrantied with the electronic trolling valves. With Yanmar, you are limited to mechanical trolling valves and my understanding is they invalidate the warranty on the gears.

Again, the technology with the QSB's was just amazing. But who knows, that could be a double edged sword.

I'm expecting to get some performance estimates from the Cummins distributor on Monday for the QSB in the 230, 305, and 330 hp options. I'll post those here when I get them.

I'm still undecided, but I think my decision will come down to the performance numbers of the QSB 230hp vs the Yanmar 6LP at 315hp. I'm looking for the package with the best efficiency at 20-22 knots that can give me a sustainable high cruise of 24-26 knots.

Yanmar's option at this point is limited to the Tier II 315 hp 6LP (which I'm told arrives in May). They will no longer have the 6LP available in the 260 hp option. The Cummins 6 cylinder QSB at 230 hp seems to be a much smoother engine than the Yanmar 4LH and therefore would be my option in the lower hp range. The Yanmar 4LH is no longer available anyway as Yanmar is replacing it with the BY series (although I wasn't considering the 4LP because of the more clattery tone it has).

I think deep down I'm hoping the additional two cylinders in the QSB 5.9 at 230 hp will give enough additional torque (versus what the 4 cylinder Yanmar 4LH had) to give me a high cruise in the 26 knot range in a 230 hp engine. In the meantime, I'm going to try to get on Emmit Yeazell's B31 again to listen to how quiet his Yanmar 6LP's are. I remember thinking he had gas engines when I got on his B31 while it was idling.

I wish the answer would jump right out at me, but I think this will come down to the quietness of the Yanmar versus the efficiency and technology of the QSB. That is going to be a tough choice for me if that's the case.

We'll see.

[IRGuy]

Bruce...

Are you sure you don't mean "Rue Paul fro president?"

[Gary Aydelotte]

My name is Gary,Im looking at 1972 B31,powered with 210 hp 3208 cats,is that a good power pack .I know it won't set any speed records but should last a long time and pretty good on fuel.They have 1100 hrs on them now and were installed 1995. thanks

[bob lico]

bruce i guess i missed the point.look at a drag boat fixed shaft angle at 200mph right!!! it don`t care if the race boat has outboards the lift cylinders are removed and the engines are bungie to the trasom.v-drives don`t touch the drive trim every racer tranfers fuel fore and aft to water condition with trim tabs going into a turn.you attain more speed with a fixed 12 degree angle then the dumb pockets because #1 you have dramaticlly increased the "wet area" over the riding on the stock strake.#2 the prop is turning in a fiberglass half circle the water turbulane is tremendous .there is white water all over the place this nolifies any advantage gain by reducing the angle.change the balance point of the boat to match the increase hp.rule #1 keep the prop in blue water will far exceed any lame ideas of taking a sawsall to the bottom.that is what i meant by no race boats have dumb pockets.i would love to have you enter jupiter inlet with waves coming at you from every direction you can feel that deep v stay in a groove compared to the dumbpockets.after we make a sale we have to take the customer out for a wild ride then give him the wheel and the payment book!there is no doubt about taking a whack out of the bottom in a following sea.i will slow my boat down to 30 knots wot and 28 cruise.just wanted to play with it to see what it could do.there is no way i could attain that speed in 80degree air temp and 70degree water temp plus additional 2500lbs.

[Bruce]

Gary,
The Cat naturals are a good engine. While not overly fast, their weight provides a little better ride.

Only downside to the Cats is the ability to rust. Pan and oil cooler housing on the left lower, under manifold side.

I've seen those engines with care run over 18,000 hours. Sitting is not good for any marine engine.

Bob,
I think we agree on most points. We'll leave it at that.


IR,
No. I mean Ron Paul.
Dr. Paul is the leading spokesman in Washington for limited constitutional government, low taxes, free markets, and a return to sound monetary policies based on commodity-backed currency. He is known among both his colleagues in Congress and his constituents for his consistent voting record in the House of Representatives: Dr. Paul never votes for legislation unless the proposed measure is expressly authorized by the Constitution. In the words of former Treasury Secretary William Simon, Dr. Paul is the "one exception to the Gang of 535" on Capitol Hill.

John,
The display information on the QSB or for that matter any of the pure electronic diesels is overwhelming at times. But if someone is a stat guy, they'll love it.
Just scrolling thru the display screens would give any XL pusher the warm fuzzies.

The 6lp will be quieter thru out the whole rpm range.

While I am not an authorized Cummins dealer so I don't do warrantee work, Cummins does send me repowers(I don't ask).
Thru the grapevine around here, which is not all that reliable at times, the QSB have been having computer problems.

Ask current QSB owners in your area that have had them in use and do a google search on QSB problems.

Research before you buy.

[Capt. Mike Holmes]

Dr, Paul - a gynecologist - is my Congressman. Years ago, the feds were billing me for a sutdent loan I never had. They had collection agencies and attorneys threatening me every week. I convinced them all that they were after someone with basically the same name, but a different address and SS#, but they just gave it to a different collector and kept after me. Uncle Vic advised me to write my congressman, so I did. Within a week after Dr. Paul's office contacted them on my behalf, I got a letter of apology, and have not been bothered since.

Paul is also on the side on the fisherman in a lot of the conflicts with NOAA Fisheries. I have a copy of a letter he sent Dr. Roy Crabtree calling for his and Dr. Hogath's resignations over the red snapper mismangement fiasco, and inviting them to appear before congress to answer questions about why snapper had been managed into such scarcity. Paul is also known as "Dr. No" in Congress, because of his voting habits. He runs as a republican, but admits to actually being a libertarian.

I do not agree with his views on the war (bring 'em home, right now), and he doesn't stand a chance of getting the republican nomination for president, but otherwise I think he's one of the good guys.

[Sean B]

Uncle Vic advised me to write my congressman, so I did. Within a week after Dr. Paul's office contacted them on my behalf, I got a letter of apology, and have not been bothered since.

That really works? I never thougt to contact a congressman with a problem. What do you do, say "hey I voted for you so please help me out with this problem?"

[In Memory of Vicroy]

Sean - that's exactly what you do....Members of Congress have huge staffs to deal with their voters' problems with the federal government...its a tried & true vote buying tool. They all have multiple offices in their home districts for doing this stuff.

Back to the topic of speed and diesel h.p., my view remains, like many others, that anything over 300 hp a side is pretty much a waste in a B31. On the other hand, it takes about 240 a side minimum to make the boat perform right. Almost all of us with diesel B31s in that hp range get cruise speeds in the mid 20kt range with teriffic economy and because we run pretty large diameter wheels, we get great low speed handling. The lower rpm diesels like Cummins, DD & Cat seem to do better with 1.5 gears and the higher speed ones like Yannie & Vulva seem to do better with 2:1.

Lest we forget Paul's engineering analysis early on years ago on this site on the efficiency of diesels with hp, gearing, and props, the larger diameter prop you can turn, the more efficient the set up.

AJ was one of the more efficent Paul (Capy to most of us) calculated. AJ has Cummins 6BTA 250s, 1.5 gears, and 21x22 three blades with no cup. She is heavy, I estimate 13,000#. She runs 24.5 kts at 2400 rpm all day, regardless of load, and I mean regardless of load. Full fuel, couple hundred # of ice, 13 guys and all their gear, still 24.5 kts. Yesterday I took her for a cruise on the Tickfaw River, just me & two lovely ladies, and she went from 1000 rpm and 7.3 kts to 2650 and 27 kts in a mere 6 seconds.........underpropped, but that's the way I like her....pulled her back to 2400 and settled right on 24.5 kts, smooth as a baby's posterior.....you can cover a lot of water at 24.5 kts with the engines loafing along, sipping fuel at 16 gph total......

I looked into the 305 hp QSB 5.9s for sport, and they go for about 25k each and have a belt driven water pump. You can minimize the smoke on the mechanical engines like mine by using block or pan heaters to help with start up and not letting them idle cold - get some load on them as quickly as you can. Once they are warmed up they produce virturally no smoke or smell. Control the clattering with Soundown. Huge, simple, dependable chucks of iron that anyone can do all the maintaince on, and parts are cheap.

Anyone want the hear the recipe' for my garlic stuffed Boston Butt pork roast?

UV

[In Memory Walter K]

Vic- Of course.

[Sean B]

Sean - that's exactly what you do....Members of Congress have huge staffs to deal with their voters' problems with the federal government...its a tried & true vote buying tool. They all have multiple offices in their home districts for doing this stuff.

Thanks, I didn't know that. Next time I have a problem with something I'll give it a try. I also wonder where the money for all the staff time and office space comes from.

[IRGuy]

Bruce..

I was only yanking your chain!

Actually I had never heard of Dr. Paul, but from what you guys say above.. he is exactly my kind of politician!