Prop Pockets??

BlueChip · Post by **BlueChip** » Sep 12th, '07, 16:03

I heard a guy talking about putting in Prop Pockets in a B31. Any one ever heard of this? Has it been done? Make sence...? 3'1" isnt much any way... but i guess with pockets you could get down to under 2'6"?

Just curious.

Chris

CaptPatrick · Post by **CaptPatrick** » Sep 12th, '07, 16:21

Chris,

The only prop pockets for the B31 are made by Cabrera in Miami. They were needed to lessen the shaft angle on B31s powered at 350 hp & above...

A 31 Bertram with anything over 320 hp is lunacy.

The prop pockets & special struts/rudders are expensive, the installation is double expensive, the net gain in efficiency is less than spectacular, and powering a B31 to exceed 32 kts becomes a dangerous proposition. The hull speed of the 31 is 35 kts & even at that speed the boats starts getting squirrelly

With a stock 15 degree shaft angle & 300 - 320 hp, you'd have a boat capable of over 30 kts WOT and cruise at 27 - 28 kts on calm water. In the open ocean, you'll rarely be able to cruise a 31 much above 22 kts without breaking things.

Br,

Patrick

In Memory of Vicroy · Post by **In Memory of Vicroy** » Sep 12th, '07, 16:50

Ditto what Patrick teaches. The only B31 I ever saw up close with prop pockets was the one Classic 31 built outside of WPB. Cat 3116s at 350 hp. Agree a lot of work and money for little gain. Another drawback is your differential steering using just the gears is cut way down, and one of the finest attributes of the B31 is its ability to spin on a dime and back down, all due to the wide stance of the props and the fact they are in clean water and get a lot of bite. One of the myth "knocks" on the B31 was it did not back down well....gee, someone better tell those Captains at TSL you can't chase billfish in reverse at 12 kts in a B31....they do it with precision.

On the other hand, our own Scot has put a prop pocket in his project B25 and putting a single 6V71TI Detroit oil slingin' dump truck motor in her....different deal, but interesting.

UV

Bruce · Post by **Bruce** » Sep 12th, '07, 16:51

I will add to what Pat said,

Repowered both stock and prop pocketed 31's.

Standard- Yanmar 6LP 315hp 33 knots wot.

Prop Pocket- Cummins QSC common rail 330hp 34.9 wot.

Estimated cost to be able to swing the extra prop for a 1.9 knot gain, $14,000.00.

ianupton · Post by **ianupton** » Sep 12th, '07, 17:54

John Patnovic at Whorton Creek Marina also put in prop pockets in one of the B31s that he redid.

He apparantly consulted with Hunt Yachts for the engineering side of it.

I was never in the boat, but he swore that it ran like a champ.

Ian.

BlueChip · Post by **BlueChip** » Sep 12th, '07, 18:56

i was thinking for of the shallow draft aspect of it. My dad is lookign for a sportfish with less than 3 feet of draft..... he wants a jet boat Hinckley and i want him to get a sportfish for obvious reasons number 1 being Fishing....

The Hinckley 44 draws 2'2" ..

i sugested a B31.....

I figured just cause i cant afford one right now doesnt mean i cant get Pops to buy his own (and just use it like my own)

Chris

nic · Post by **nic** » Sep 12th, '07, 19:18

Squirrelly?

ianupton · Post by **ianupton** » Sep 12th, '07, 19:58

I know that hull form, etc plays a huge role here... but... The B20 and B25 do not seem to get squirrely at these speeds. Perhaps it is the difference between a little chine walking in a B20 to a B31 walking abit.

I was out last weekend in a B25 that was repowered with a single Mercruiser 496 HO Bravo III. The boat was very 'lively', but I wouldn't have said squirrely. She ran an honest 50 mph in not ideal conditions. (Slight chop, 4 adults and 2 kids on board).

Ian.

Raybo Marine NY · Post by **Raybo Marine NY** » Sep 12th, '07, 20:07

where is Craig Mac and his hot rod 31 that hits over 40 when you need him?

CaptPatrick · Post by **CaptPatrick** » Sep 12th, '07, 20:08

Ian,

It's hard to draw parallels between different hulls...

The B31 has more weight and a higher center of gravity than the 20, 25, & 26. Also a more exaggerated chine. In calm water Da' Judge's B25 will run rings around a B31 with 1/2 the horse power...

Br,

Patrick

nic · Post by **nic** » Sep 12th, '07, 20:12

Ian,

I just love that shot but I think it has more to do with a banking turn to port than chine walking.

I don't have any high speed experience of the 31 but they were a successful race boat until the skinnier Aronow hulls and back then must have been going a lot quicker than 35 knots. I recall seeing a pic of a world water diesel speed attempt in Miami in a 31.

Capt Pat,

I think I read that an over-powered 31, was that Grim Reaper, had trim problems that made her squirrelly? Bob Lico is getting 38 knots isn't he? Is it more to do with bow-down attitude than an actual hull speed limit?

Nic

Raybo Marine NY · Post by **Raybo Marine NY** » Sep 12th, '07, 20:15

im trying to get Bob with his oil burners to race Craig and his stock big block gassers, no luck yet.

Craig has weight on his side, boat is VERY light.

John F. · Post by **John F.** » Sep 12th, '07, 20:28

I've seen the Patnovic boat with pockets. I think they put 440 Yanmars in her. I've never seen her run. My only experience w/pockets has been on a 31 Tiara. Nice boat, but the props ventilated a pretty lot when it got snotty out. I love speed---and if I want to go fast, I'll get something designed for it like......The B31 is a great fish boat--leave it be.

CaptPatrick · Post by **CaptPatrick** » Sep 12th, '07, 20:42

Nic,

"Grim Reaper" wasn't squirrelly, it was just over powered, big wheels, stock shaft angle, making it a pig at 29+ kts. At that speed, it just nose dived and started plowing water. I don't think that boat would ever see 35 kts with the way it was setup. Prop pockets would have helped that boat, but again it's a case over powering.

Yes, a B31 is capible of doing over 35 kts, Regino Cabrera has had one up to 50 mph, verified with a radar gun. Later the same boat chine walked at around 40 kts, (owner operated), made an instaneous hard turn, throwing one bridge passenger over the dash onto the fore deck and breaking his clavicle. Big law suit....

What I've always said is that a B31 doing speeds above 35 kts is dangerous. Are people going to stop trying to turn a B31 into a go fast boat just because I say it's dumb?? Not on your life! There are still plenty of us who drive without seat belts & ride motorcycles without helmets. I'm one of them.

Safety is, or should be, a mater of personal choice, not mandated statutes...

When are we going to see pics of "Tennesse"?

Br,

Patrick

bob lico · Post by **bob lico** » Sep 12th, '07, 21:25

i am not getting into a pissing contest over prop pockets.in MY opinion
you are destroying the intergrity of the perfect hull bottom.must important if the captain himself was not doing the glass work on those prop pockets you would be playing russian roulet.lets talk about last sunday coming off a 7' wave in the inlet no lets not.
nic speed in a 31 is all about perfect plane angle if you are using trim tabs-------------wrong.nic at 38 i was experimenting,the boat was totally strip down not even a cockpit sole.and 350rpm over max rating.loaded up i am lucky if i do 30kt.i detuned the cummins and downsized the prop pitch by 4.however the boat is on plane in 5 seconds, i imagine it is due to the vulcan drives.the boat did not nose in whatsoever at 38 as a matter of fact the chase boat only 10' away said i was dead level but riding on the bottom strakes.why in gods name would you put prop pockets in!!!!!

JP Dalik · Post by **JP Dalik** » Sep 12th, '07, 21:38

Been to the Hudson a pile so far twice in the last two weeks once on Sept 2 once on Sept 7. Average speed going and coming from the 82 mile average... 14 kts.
Gotta tell ya I don't care how fast she'll go in the flat it's what you can do in the real world that counts. We can run 29kts in the flat @ 2550 but I dare you to try it in the real world.
We got little boats in a big ocean.

bob lico · Post by **bob lico** » Sep 12th, '07, 21:41

amen!!!!!

scot · Post by **scot** » Sep 12th, '07, 21:56

Gotta jump in...

IMHO the primary difference in the 20, 25 and the 31 is that all of the 20 & 25's have the engines placed at or near the stern. This allows a lot more of the hull to "get free" of the water at high speeds. The 31's mid-ship engines creates a better balanced hull and a great cockpit for fishing and Howdy boating, but the 20 & 25's go fast with a lot more grace...again aft mounted engines.

This is basically the only difference I can find because all 3 of the hulls have nearly identical lines. In fact in a length vs width ratio the 25 is a bit wider hull. Napier hulls (26,28, etc) different story.

Pockets are like everything else, there are good ones and there are bad ones. Hull integrity is not an issue when constructed correctly with epoxy resins. My last pocket conversion was run a ground, hit a steel pipeline, flies through the air, etc. with only prop damage....no structural damage at all.

IMHO the key to pockets is to use them to create the required shaft angle and engine location. Keep the recess area to a minimum and there's really no reason to pocket a 31 hull. There is a huge difference in a twin with pockets and a single with a pocket....the twin pockets are high and easy to cavitate, a single is buried in the keel and if the aft section of the keel is "finding air" your going to fast for these hulls.

nic · Post by **nic** » Sep 12th, '07, 23:41

That all makes good sense, thanks.

Finally got the Tennessee back from a small yard up the coast and ran into the start of a developing storm, 15-18 knots until we got what felt like air-borne. Throttling back into the more vertical faces the best thing was powering up off the back of the waves, weaving between the crests, the grip on the water with the deep 4-bladed props - a very secure feeling.

Going out tomorrow for the first time in almost three months, pics will follow soon after!

Nic

John F. · Post by **John F.** » Sep 13th, '07, 05:57

Scot-

My comment was directed at pockets on B31s. It seems the reason is to make them a 40 knot boat rather than a 30 knot boat. I just don't see the wisdom in that. Your 25 pocket looks like a work of art. When Carolina Classic starting putting a straight inboard in their 25, they went with a pocket (I really like the CC 25). Same with lots of the small single inboard fish boats. I really like the idea of a B25 with a single inboard diesel, but there's no way I could pull off what your doing. Yours looks great, but modifying a 31 hull? Not for me...

John

Dug · Post by **Dug** » Sep 13th, '07, 07:04

Blue chip,

Try a Hunt. My father has a 36' that has a jet and draws very little water. Remember that doesn't mean you can go in shallow water as it really is a 880 hp vacuum cleaner in jet.

But they make a really nice 25 that doesn't draw much.

Dug

Bruce · Post by **Bruce** » Sep 13th, '07, 08:22

Wrong boat to install pockets to reduce prop exposure for shallow running.

Rawleigh · Post by **Rawleigh** » Sep 13th, '07, 12:17

Wouldn't want to turn mine into a Penn Yann!!!! Yuck!

joeh · Post by **joeh** » Sep 14th, '07, 18:45

Guys,

My boat is Slainte the 2nd one Patnovic did. 330 Cummins and it is perfectly powered as many of you have said about other boats. I also saw the one with prop pockets that he did. I believe the owner spent 300K for the boat,

I would tell your dad to by a Hinckley instead of changing a boat for a foot of draft. They are great boats too.

bob lico · Post by **bob lico** » Sep 14th, '07, 19:45

raybo marine; robbie the amount of work to get it back to speed would be enormous. removing the 7100 fi pump then bench it to recalibrate to 375 hp along with the go fast changes would be in your world like repainting the boat in addition to a big drop in fuel economy you just can`t dock a boat into a tight slip at 14knots!.no thank you i will leave well enough alone.

JP Dalik · Post by **JP Dalik** » Sep 17th, '07, 18:37

Bob-Sissy,
Smoke her back don't mind the crack.
What good is the power if you can't use it?

bob lico · Post by **bob lico** » Sep 17th, '07, 19:20

honest jp i really did every thing i could.my slip is a end slip and a grady-white with a bow pupit sticks out so i cannot pull parallel into the slip.i wish i lived on the water so i could just pull in.that is not the case and docking with 1 engine in the wind is damm near impossible.do you think for one minute i enjoyed detuning that monster as well as putting that fi pump back in next to the gen!!!one thing i learned that raked prop really worked,trim tabs are you out of your mind how about bow planes like a submarine that would help.put the pedal to the metal with 1200 lbs of torque and the boat leaps out of the water on plane is seconds,but you can`t dock it or for that mater i will never beat your 6 year old daughters rock fish at 14 kts how could i troll?

bertram31.com

Prop Pockets??

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