The amazing DP

[Morgan's Cloud]

Well , do I have your attention now Randy ?

First off I'd like to add my voice to the many before me who have thanked Big Grizz for his help. He is a tremendous resource to the board .

It was a bit of a well kept secret for the last 12 months or so but the outcome may be of interest to all of the detail oriented technophobes here.
When I finally re-launched the St Tropez last year after it's complete and total rebuild / repower I was horrified at its new 'manners' , or more appropriately , the total lack of !
It was a complete pig ...no , worse , a BEAR .
It was so bad that I hated driving it , and instead of making up for 5 years out of service I barely put 25 hours on it and didn't even put it over this summer.

When I repowered I assumed that the DP unit would be massive overkill on a light 19' boat , so I went with the single prop unit , Volvo's newest the SX-A. The engine is the 5.7Gi , Volvo's counter to the Merc 350MAG .
Even though I finally had a working front fuel tank to help as 'ballast' the bow was so light that it was a constant battle keeping the boat on the water , there was real potential for a blowover !
It wouldn't track in a straight line even in calm weather .. don't even talk about a slight breeze with a broken water surface.
The boat heeled to port as soon as you jabbed the throttle from a fast idle and once on plane you had to maintain port tab to keep it level.
Unfortunately the second you met an oncoming wave the bow would rise slightly and the boat would come crashing down on the flat of the port bottom.

Always porpoising even in corners, the trim couldn't even approach neutral which exacerbated the prop torque.
Turns were a hair raising experience in both directions with the boat bucking , kicking and slamming through them all .
Trying to maintain a straight course at cruising speed with any breeze whatsoever was impossible and I was constantly adjusting the trim tabs to compensate .

What had happened to my baby ?

I know from this site that many a boat has been tamed with the 'prop treatment' from Randy so I PM'd him and arranged a prop to try out.
I would assume that he sent me what he would have considered to be the optimal starting point , I believe it was a Turbo 1 .
Well , the boat might have been marginally smoother and the exhaust note was a tiny bit different (through the leg) but otherwise , no different .
One prop test , out about $500 and still no different. I was very skeptical that a prop was going to fix this and after much rationalising I arranged for Doug Russell in Worcester to send me a DP to test out .
Well , I'm just back from a 2 week break and I did have a day that was suitable for testing. We put it on the trailer and took it to a ramp nearby and over I went.

As soon as I put it in gear I knew something was going on...
I doesn't even hunt at low speeds any more ! The transformation is just amazing , I couldn't believe it . My baby is back .
The feeling of 'security' is fantastic .. turns in either direction are smooth and predictable , no more heeling to the port side , hell , I didn't even touch the tabs during the test and there was a fair breeze blowing too .. the boat didn't fall into the wind when running abeam to it ...
To say that I'm happy would be an understatement.
It wasn't cheap but I couldn't sit back and leave it like it was and chances are that I could have easilly spent $5000 plus on prop testing and still not seen any improvement ..

Oh , by the way , besides the very interesting fact that this was a real life test on the SAME boat not two 'identical' boats from the same manufacturer but with different power packages , there is one other interesting bit of data ..
The old SX-A 1.51:1 gears swung a 21" prop at just about dead on 5000 rpm. The boat was so out of controll that I was unable to gps it , but the speedo which is dead accurate from 0 to 31 mph (that's as high as I was able to gps test it last summer) showed a comfy 60 .
The DPS-A has a 1.95:1 ratio and swings an F8 propset (whatever that is ) at 4700 .... The speedo is showing 62 + ....... pretty cool huh ?

Now lets eee if I can attach a few pics to make this post interesting ......

[cutwater]

I am drooling over this one... I have wanted a DP for so long for the Minx, at some point I will have to do it. Good for you for taking drastic action. That looks fantastic and now it handles well, too. Congrats! Any more pics of the boat you can post?

[BigGrizzly]

I am really happy for you. I know how you love this boat. I am still a little at a loss, the prop should have helped. Like I have always said every boat is a little different. I do know the DP does solve a multitude of problems. We did try to save some money but it wasn't meant to be. The good part is you have a boat that is nice and is a keeper. I am glad you kept at it. It will be worth it in the long run.

[Ghost]

Interesting stuff. I have often wondered why more people don't repower Donzis with duoprops. When I have heard complaints about handling, whether here, in published reviews, whatever, most of the things I heard sounded like things a duoprop might cure.

I can imagine everyone here stuffing a bar of soap in a sock and beating me senseless for even saying this, but it seems logical to me.

(I seem to recall a period when Donzi offered Volvo as well as Merc drives, no, but I don't think I've heard more than about two people on the site talk about having Volvos.)

I'm curious what people think about the pros and cons of duoprops for boats like the Classics or other Donzi single engine setups 25' and under. Again, I'm not saying what is better--I don't know. I am just asking. But I always thought if I were going to have a 22 Classic, a Volvo 420HP big block with the high-speed duoprop drive (can't recall the desingator anymore) would be an ideal set up.

Comments are welcome. I am donning a helmet...

[CHACHI]

TONY SPORER, WE NEED YOU.

Ken

[cutwater]

But I always thought if I were going to have a 22 Classic, a Volvo 420HP big block with the high-speed duoprop drive (can't recall the desingator anymore) would be an ideal set up.

DPX... and I want one...

TONY SPORER, WE NEED YOU.

Ken

This Tony?

"1996 22' Classic
Volvo Penta 7.4Gsi/DPX
bone stock 71.8 gps mph"

not bad

[Conquistador_del_mar]

Well , do I have your attention now Randy ?


What had happened to my baby ?

I know from this site that many a boat has been tamed with the 'prop treatment' from Randy so I PM'd him and arranged a prop to try out.
I would assume that he sent me what he would have considered to be the optimal starting point , I believe it was a Turbo 1 .
Well , the boat might have been marginally smoother and the exhaust note was a tiny bit different (through the leg) but otherwise , no different .
One prop test , out about $500 and still no different. I was very skeptical that a prop was going to fix this and after much rationalising I arranged for Doug Russell in Worcester to send me a DP to test out .
Well , I'm just back from a 2 week break and I did have a day that was suitable for testing. We put it on the trailer and took it to a ramp nearby and over I went.

As soon as I put it in gear I knew something was going on...
I doesn't even hunt at low speeds any more ! The transformation is just amazing , I couldn't believe it . My baby is back .
The feeling of 'security' is fantastic .. turns in either direction are smooth and predictable , no more heeling to the port side , hell , I didn't even touch the tabs during the test and there was a fair breeze blowing too .. the boat didn't fall into the wind when running abeam to it ...
To say that I'm happy would be an understatement.
It wasn't cheap but I couldn't sit back and leave it like it was and chances are that I could have easilly spent $5000 plus on prop testing and still not seen any improvement ..

Oh , by the way , besides the very interesting fact that this was a real life test on the SAME boat not two 'identical' boats from the same manufacturer but with different power packages , there is one other interesting bit of data ..
The old SX-A 1.51:1 gears swung a 21" prop at just about dead on 5000 rpm. The boat was so out of controll that I was unable to gps it , but the speedo which is dead accurate from 0 to 31 mph (that's as high as I was able to gps test it last summer) showed a comfy 60 .
The DPS-A has a 1.95:1 ratio and swings an F8 propset (whatever that is ) at 4700 .... The speedo is showing 62 + ....... pretty cool huh ?

Now lets eee if I can attach a few pics to make this post interesting ......

I'm glad to hear that the DP made such a positive difference! When you virtually eliminate steering torque, the boat can handle so much better overall. Bill

Interesting stuff. I have often wondered why more people don't repower Donzis with duoprops. When I have heard complaints about handling, whether here, in published reviews, whatever, most of the things I heard sounded like things a duoprop might cure.

I can imagine everyone here stuffing a bar of soap in a sock and beating me senseless for even saying this, but it seems logical to me.

(I seem to recall a period when Donzi offered Volvo as well as Merc drives, no, but I don't think I've heard more than about two people on the site talk about having Volvos.)

I'm curious what people think about the pros and cons of duoprops for boats like the Classics or other Donzi single engine setups 25' and under. Again, I'm not saying what is better--I don't know. I am just asking. But I always thought if I were going to have a 22 Classic, a Volvo 420HP big block with the high-speed duoprop drive (can't recall the desingator anymore) would be an ideal set up.

Comments are welcome. I am donning a helmet...

I will be restoring a 27' Magnum sport starting this winter. One of the first things I decided was to go with a single engine and Bravo III drive for better handling so I would not have to install external steering. I am figuring on about a 500HP engine to get the speed I am after which the drive should be able to support. When I first dreamed up this project, I thought it was a little radical, but I have since learned that it works in practice. I will never get radical speeds out of the setup, but I should have a great cruiser on our relatively large lake (Lake Texoma). I will eventually be able to report the results. Bill

[Morgan's Cloud]

A few more thoughts...
Cutwater ... Probably won't be able to get any decent photos of the boat untill later next spring ... Although I could temporarily set up the interior and climb a tree to get a decent shot
I wonder about going through the effort to change to a DP unit if your boat already handles OK with a single prop unit. Bear in mind , in my case it was a total resto / repower . I just asked for the 'wrong' outdrive when I put together my package !
Funny thing is that before the resto , I ran this thing for nearly 20 years with a 351/Alpha setup and it had no issues at all.
Maybe this all stems from the fact that the new engine is so much more potent.
When you think about it though , I would guess that our small boats with high power to weight ratios are perfect candidates for the DP unit.
Remember , the unit I have doesn't bear too much resemblence to Volvo's first DuoProp that was introdcued in 1982 . You know.. the units that were responsible for the 'you loose at least 10 MPH' reputation
Ghost ... When you say you don't hear of many people here using Volvos , I presume you mean the DP units ? In that case , yes . I can only think of 2 others , only one is the high perf DPX and there was another St Tropez that had a B3 installed with a turbo Yanmar.
Otherwise , a large percentage of the pre -82 or so classics were Volvo 250's and 270's.
Randy , after 21 years + with this thing , I think we're joined at the hip ..
Even though it was a total mess when I had it delivered in April 1987 , I knew it was a keeper !

[CHACHI]

DPX... and I want one...



This Tony?

"1996 22' Classic
Volvo Penta 7.4Gsi/DPX
bone stock 71.8 gps mph"

not bad

Yes, that Tony.

Ther is another board member, McDonzi, who also has a big bolck with a DP hangin' off the transom.

Ken

[Morgan's Cloud]

Bill , have you investigated wether Merc actually offers a 'higher performance' range of B3 props ?
I can tell you first hand , the VP propset I'm running bears no resemblance to the Merc B3 props at all .
Of course you know that I have the 502 B3 in the Magnum , but we never ran the boat before we restored it so we don't know what benefits the B3 provides for it. If it is however , like what I've just experienced in the St T , well we made a good choice then !
Steve

[Morgan's Cloud]

[QUOTE=BigGrizzly;480238] Like I have always said every boat is a little different./QUOTE]

This is very important to remember, I hope no-one overlooks it .

[Ghost]

Ghost ... When you say you don't hear of many people here using Volvos , I presume you mean the DP units ? In that case , yes . I can only think of 2 others , only one is the high perf DPX and there was another St Tropez that had a B3 installed with a turbo Yanmar.

Otherwise , a large percentage of the pre -82 or so classics were Volvo 250's and 270's.

Exactly, yes, I was not specific enough-I meant Volvos with DP units. Thanks.

One other question--am I losing it or did Donzi (for some time in within the '88-'97 range maybe) offer both modern Volvos and Mercs? I would swear I dropped by my local Donzi dealer and saw both available on several occasions, but maybe I'm smoking crack. (Regardless, even if they did, it sounds like very few took them up on the Volvo option.)

Last, I'm probably missing something simple, but does anyone know why Donzi doesn't offer the Classics with the Bravo 3 option, even if they don't work with Volvo? (Can you special order it? Hard to imagine you couldn't but not seeing it on the website makes me wonder...) Does top end suffer or something? I'll be the first to admit I know very little about real high-performance engines and drives, and though I hear a lot about lots of other projects here, the silence on counter-rotating setups is pretty deafening, making me wonder. (Of course, the two comments I have heard about DPs have been *extremely* positive, making me wonder even more why more don't do it.)

Regards,

Mike

[Ghost]

I will be restoring a 27' Magnum sport starting this winter. One of the first things I decided was to go with a single engine and Bravo III drive for better handling so I would not have to install external steering. I am figuring on about a 500HP engine to get the speed I am after which the drive should be able to support. When I first dreamed up this project, I thought it was a little radical, but I have since learned that it works in practice. I will never get radical speeds out of the setup, but I should have a great cruiser on our relatively large lake (Lake Texoma). I will eventually be able to report the results. Bill

Cool--I'm interested to see how it turns out for you. The efficiency of a single over twins is what, maybe 20% or so in HP? The weight savings is going to be about a half ton, right? Admittedly, nowhere near the cubes of twins, but I wonder how it will compare, say, to a pair of 300HP small blocks for top end.

(If I say the word "bow-thuster" will I get stoned to death? Now that I think about it, is it in any way unsafe to put a bow thruster on a performance boat, given the speeds at which you might stuff the nose? If there's a problem there, anyone have a rule of thumb about what speed is too much? 60? 70? ...)

Regards,

Mike

[f_inscreenname]

A bow thruster on a performance boat? I would think it would take to much of a beating at speed and maybe a little to much odd pressure on the bow but what do I know.
I just read this thread for the first time. Morgan’s Cloud I have a question and I hope you will be honest. No judgment from me but I have to know. You say you picked up 2 or 3 mph and some handling over your last set up. On your old set up did you do any prop testing to help the handling? Left and right hand props? I ask because my boat is a “bear” with a right hand prop on it (enough that it broke a steering cable) but with a left it’s like it has power steering from start to WOT. But like said all boats are different.
Now here is the real question. How much did it cost for those couple mph? Motor and DP are not cheap.

[zelatore]

Cool--I'm interested to see how it turns out for you. The efficiency of a single over twins is what, maybe 20% or so in HP? The weight savings is going to be about a half ton, right? Admittedly, nowhere near the cubes of twins, but I wonder how it will compare, say, to a pair of 300HP small blocks for top end.

(If I say the word "bow-thuster" will I get stoned to death? Now that I think about it, is it in any way unsafe to put a bow thruster on a performance boat, given the speeds at which you might stuff the nose? If there's a problem there, anyone have a rule of thumb about what speed is too much? 60? 70? ...)

Regards,

Mike

Your boat is what - 28'? That's a great size for a BB single and duo-prop. And I think many here would tell you (yes, it's arguable) that Volvo makes a better dual-prop drive than Merc.

As for a bow thruster....Oy! What are we going to do with you??

I've never seen one in a performance boat. Heck, I've rarely seen them in boats that small. I know it's been done, both aftermarket and OEM. You'd need to find room for a 6" tube, the motor, and an extra battery all in the bow. I suppose you could do without the battery, but that would mean running some serious cables the length of your boat, and it would be easier to run smaller cables for charging and a small gp24 battery close to the thruster motor. That's also a bit of weight in the very front of the boat.

The fastest boat I've driven with a thruster was a 28 Four Winns with twin 5.0 Volvos. About 47 mph. It was an aftermarket installation, and made no noticeable impact on the boat, but then again it was far, far from a performance hull.

I hope you've got a pocket full of sheckles if you're thinking about installing a duoprop drive and a thruster. Those two will make a blower look cheap.