Bravo III XR performance.......

[Donziweasel]

Nevermind.

[Morgan's Cloud]

Have you seen/read any of my posts on my B3 and Volvo dp experiences ?
I hate internet echo .

[Donziweasel]

I haven't been around much the last few years, so I must have missed it. I will delete this thread if you like.

[Carl C]

There will always be "internet echo" and usually some fresh input and opinions. Some links might have been helpful. How many times have oil and prop threads come up? I usually learn something new each time; Or at least confirm that I'm doing it right.......

[Morgan's Cloud]

No, seriously I don't mind re-stating as long as it doesn't sound like a broken record to some people.

First off, Tony has the 22C , now for sale , that was rigged with a 385 DPX package from the factory. He has waxed eloquently about it's handling often. Actually , I'd love to know if he's also driven a MAG B1 package so he can make the direct comparison.

In my case we re-powered the Magnum with a 502 B3 package but because it was a basket case when we got it , we had never driven it before so we don't have a basis for a before and after comparison. My belief that it handles extraordinarily well was confirmed when our mechanic went nuts over it's performance. As a former racer and builder and ace mechanic who's driven everything I take that as a fair testimonial.

When the restoration on the St T was finished I dropped in a new Volvo 5.7 package with the new single prop SX-A unit. This would be Volvo's version of the 350MAG / B1 unit.
To my horror the boat was virtually undriveable. Randy sent me a prop that he thought would settle things down but it made no difference at all.
I ended up biting the bullet and switched the unit out for a DPS-A.
The difference was like night and day . Just unbelievable .

Now , a lot of people will say that the B3 isn't as fast as a B1 but it's probably not a fair comparison to bring Volvo into it. The DPX and DPS-A units are hydrodynamically faster than the B units.

If you're toying with the idea of going dp on your new project please let me know and I'll gladly expand on my opinion .

[joseph m. hahnl]

I think you need to look at what the deign intent is. No I haven't personally talked to the engineer and I have no real word experience with twin props . So if I was to guess, they are for weight, heavy boats that need big pitch to go fast and a little pitch that would give it a prayer of getting on plane. Now you put it in a light 2400 LBS boat with mega pitch, prop torque listing seems eminent , The questions that comes to my mind does the short pitched slipper prop ,slip the other larger prop so it actually has a greater slip % then a stand alone prop, canceling list. How much can the pitch variable be between props, and what are the sizes available. For example if the max pitch was a 27p.it would be more cost effective to get the motor to turn a single. But in all honesty it would look BBBBBBad to the Bone

[Morgan's Cloud]

Joe, I was so amazed at the transformation in my St Tropez that in a post a while back I said that maybe the dp unit is even more beneficial for our small fast boats than originally thought.

There is NO prop torque effect whatsoever. When you jab the throttle from an in gear idle the boat does not (like it used to do) torque over to the port side .It just lunges forward perfectly level.
Chine walking ? A thing of the past ! Turns to port or starboard ? No preferential side , they're both the same.
And that annoying deep V trait of 'hunting' ... also a thing of the past.

Volvo does not reveal the sizes of their props by the way they list/sell them .They just have a number/letter combo that once you understand it means that the greater the number the higher the pitch .You just don't know what the pitch is.
I had mine scanned and I can confirm that an 'F7' set is 26'' . With Mercs they tell you the size. Interestingly , the Magnum also utilizes a 26' prop set .

There is no doubt in my mind that the St T is actually faster now with the DPS-A unit. The only question is, is that because it IS faster , or because of it's massive improvement in handling I can now explore top speeds for a bit longer ?

[Greg Guimond]

If your objective Donziweasel is top speed then B1, if your goal is to have the best all around package for handling then B3. West coast guys run the B3's all the time and love 'em. There wive's love 'em even more as they are easy to drive as has been described in detail above. My .02 is I'd just buy Tony's 22 Classic and cut the 18 loose.

[mattyboy]

MC

some interesting tests

http://www.youtube.com/watch?v=JZp_HODU104



http://www.youtube.com/watch?v=eSCJ89lczug

http://www.youtube.com/watch?v=CAk2Q20HkvY

[joseph m. hahnl]

Joe, I was so amazed at the transformation in my St Tropez that in a post a while back I said that maybe the dp unit is even more beneficial for our small fast boats than originally thought.

There is NO prop torque effect whatsoever. When you jab the throttle from an in gear idle the boat does not (like it used to do) torque over to the port side .It just lunges forward perfectly level.
Chine walking ? A thing of the past ! Turns to port or starboard ? No preferential side , they're both the same.
And that annoying deep V trait of 'hunting' ... also a thing of the past.

Volvo does not reveal the sizes of their props by the way they list/sell them .They just have a number/letter combo that once you understand it means that the greater the number the higher the pitch .You just don't know what the pitch is.
I had mine scanned and I can confirm that an 'F7' set is 26'' . With Mercs they tell you the size. Interestingly , the Magnum also utilizes a 26' prop set .

There is no doubt in my mind that the St T is actually faster now with the DPS-A unit. The only question is, is that because it IS faster , or because of it's massive improvement in handling I can now explore top speeds for a bit longer ?

26P with a stock 350? It would be faster. You should plug it into a prop calculator and get the slip% to compare to a stand alone.

[mattyboy]

Joe

the duo props run higher ratios then V8 singles 1.9 2 2.14

and when you get the slip number divide by 2


just an example in one of the test films i posted the regal 27 at 6000 rpm 54 mph and a 2.14 with 26 pitch set is at about 21% slip or 10 percent on each prop. if i remember correctly the BH ran around the same slip %

would love to see what a lighter boat that is stern weight sensitive to begin with reacts to the light weight power

[Morgan's Cloud]

The 380 is a very interesting engine package . It will be interesting to see what Volvo's lineup looks like when it is fitted in . I can understand it's influence on the 8.1 , 8.2 engines but if it's weight is as good or better than the 350's it'll be interesting to see what becomes of them too.

I never knew how to do the prop slip calculator thingy with a dp and I've never seen a site that offers the option to do a dp calculation , but Matty is right about the gearing differences.

The Mag is running a 2.0:1 ratio and the Donzi is running a 1.95:1 ratio.

If I was doing a dp installation on another smaller boat again and wanted max performance I would go with the Volvo over the B3.

Out here service is a nightmare and parts are ridiculously expensive and you have to wait for them no matter what colour your engine is. Understandably , things are a little different in the US and that has a huge effect on one's decision .

[joseph m. hahnl]

Joe

the duo props run higher ratios then V8 singles 1.9 2 2.14

and when you get the slip number divide by 2


just an example in one of the test films i posted the regal 27 at 6000 rpm 54 mph and a 2.14 with 26 pitch set is at about 21% slip or 10 percent on each prop. if i remember correctly the BH ran around the same slip %

would love to see what a lighter boat that is stern weight sensitive to begin with reacts to the light weight power

[mattyboy]

MC

I guess it is a mathematical equation that gives one an idea of how efficient the prop/s are. I always wondered how they figure for hull weight and design?????

the way I look at it a prop must have some slip a good prop is around 10% or under so when there are two pushing the same way their slip is combined ,either on one shaft or two shafts in a twin app.

[Morgan's Cloud]

I keep forgetting to bring this up .

Jim , a member with a lot of experience under his belt has a Yammy dp on his OB16
I know he's driven more than his share of boats plus he has what must be the only dp 16OB around .

It would be great to hear his experience as well .

One thing that does put me in a rather unusual situation is that I converted the same boat and engine package to a dp after running it as a singe prop unit .
So it's a true apples to apples comparison.
Not like boat tests that have run 'similar' drive packages , one Merc ,one Volvo, on the same model of boat. Just a few small inconsistencies in the build difference of the two boats alone could affect results and impressions .

edit: Matty , in my opinion it looks like Volvo has put in a lot more time/research into their dp props than Merc. There's a big difference in appearance between the two sets I run and they're both 26'' sets. That could have an effect on the end result too .