Choosing between rocks

[Conquistador_del_mar]

Bill , that green is identical to what mine originally was .... Somehow I'm thinking that you might just want to try sanding a little to the west of the spot that you already have made .... No harm, seeing what work lays ahead of you eh ?

I'm a little cynical of the speed on that 27 with the 502/B3 as my 25 is correctly propped and it may see 60 on a good day .

Of course with a little searching one can find tons of discourse on the pros/cons of twin prop units.

If we're talking solely about the B1 vers the B3 of course the B1 will have a bit of a speed advantage , but how important is absolute all out top speed to the individual owner ? Plus , you can't rule out the handling advantages.
Remember also that Merc was going to introduce a 'performance line' of B3 props.

Again , as far as the generic statement ' Duoprops cost you speed ..' goes , has anyone seen the boat tests where identically powered , identical boats are run against one another .... ? The single prop Merc drive is slower than the Volvo SX ... And that's not even taking into account the new SX-A which more resembles the DP-X .

Steve,
I will try sanding a little more. I really hope to find the hull number for quite a few reasons.
What engine, power, and drive does your 25' Magnum have? I wonder how the two boats compare in weight. For that matter, I would like to know the weight of the 27 without engines and drives - I already know it is heavy when I look at things like the 1/2" thick solid fiberglass deck. Although I recently bought a 475HP 383CID stroked SBC for a project like this, I am now thinking that I would probably be better off with a BBC which can more easily make the torque that I know this hull will need. I have a long way to go before powering it, but I like to think about it to give me a little more incentive. Thanks for the input, Bill

[BUIZILLA]

the Squadron XII ran good with a single...

[Morgan's Cloud]

Our 25 has the Mag 502 with the 2.0:1 drive ratio and swings a 26" cupped propset. With a lightish load it just about bumps on 5000 RPM .
The weights of these boats is always of interest. When ours was still gutted , and I mean gutted ... just the hull , deck and innerliner we weighed it and it registered 2646 lbs . Add a 1245 lb engine package , beautiful custom windscreen (not that huge upright OEM greenhouse) full upholstery ,all rigging, wiring and deck hardware including custom 15' one piece S/S bow rail , 2 x 27 series batteries , fuel tank , massive (very heavy) one peice engine hatch with electric lift , auto FE241 etc , I would say that we're pretty much at 5000 lb !
That's why I find it hard to believe the 27 with two small blocks weighs .. hmmm what is it now in the brochure .... 4800 lb ? ?
One thing for sure , you'll want all the cubes you can get in a single to move that thing.

[Conquistador_del_mar]

Our 25 has the Mag 502 with the 2.0:1 drive ratio and swings a 26" cupped propset. With a lightish load it just about bumps on 5000 RPM .
The weights of these boats is always of interest. When ours was still gutted , and I mean gutted ... just the hull , deck and innerliner we weighed it and it registered 2646 lbs . Add a 1245 lb engine package , beautiful custom windscreen (not that huge upright OEM greenhouse) full upholstery ,all rigging, wiring and deck hardware including custom 15' one piece S/S bow rail , 2 x 27 series batteries , fuel tank , massive (very heavy) one peice engine hatch with electric lift , auto FE241 etc , I would say that we're pretty much at 5000 lb !
That's why I find it hard to believe the 27 with two small blocks weighs .. hmmm what is it now in the brochure .... 4800 lb ? ?
One thing for sure , you'll want all the cubes you can get in a single to move that thing.

Thanks for the info. The Bravo III that I recently bought is also the 2.0 ratio so it sounds like the 26" set of props would also be close for me if I can get to the 60MPH+ range (I know where I can buy a set). I recently heard that the 27 weighed in at 5600 with twins? - I might find a weigh scale near me to find the naked weight. I agree that I might have to come up with a larger engine. I originally was thinking about keeping the weight down with the SBC stroker. Maybe I will get a better feel from someone who has tried powering the 27 with a single before I get to that point. Bill

[superhatz]

My 27 Sport with a steel triple axle trailer weighs a little over 7000lbs.

I don't know what the trailer weighs?.....any ideas?

[Conquistador_del_mar]

Aaron,
Your trailer might surprise you on weight. It all depends on what channel was used. I have a heavy duty triple axle Competition trailer under my 23' Eliminator that I know weighs every bit of 1500lbs. Fortunately it is a C-channel frame with open channel crossmembers and a few boxed in square tubing members, so it does not rust from the inside out like so many of the local trailers I see around here with boxed square and rectangular channels that fill with water and start rusting from the inside. I have had 3 customers in the past couple years show me their trailers and asking my advice on repairing them. One guy spent $1800 having his rebuilt, but the others bought new trailers. I ramble with my thoughts - lol. I wanted to pass that along, though. Back on the subject, I wouldn't be surprised if your trailer weighed 2000lbs if it is fairly beefy with steel like it should be to support as heavy a boat as the Magnum. Bill

[superhatz]

It is a C-channel...

[smidgen too]

I talked yesterday afternoon with High Life on the phone for a while. He told me that he has a friend who installed a single engine 502/415HP with a Bravo One in a Magnum 27 and got 61MPH out of it. Needless to say, that made my day since I was hoping for around 60+MPH using a Bravo III (counter rotating props) and a 500HP engine. Eventually, I might end up with more speed than I even figured. Bill

This 1975 Chris Craft 8 metre in Stockholm Svea was rebuilt with a single 496 Ho merc they say it runs around 55. When this boat was new with twins 350cu 300 hp smallblocks with Volvo drives ran 55 mph.

[superhatz]

There's a Swedish guy on the forum here that re-powered his 27 Sport with a single 496 HO I think?.....and I thought he said it would run about 56-58?

[Boatnuts]

MorgansCloud - would love to see a pic of your 25 Magnum

[Morgan's Cloud]

One day .. If I was only a bit more computer literate ... haha

A long time back MP posted a few that I sent to him but a while back I tried to locate them and couldn't .. they were here somewhere ... Maybe he has them stashed somewhere else in his own files and could pull one or two of them again ..

[Conquistador_del_mar]

This 1975 Chris Craft 8 metre in Stockholm Svea was rebuilt with a single 496 Ho merc they say it runs around 55. When this boat was new with twins 350cu 300 hp smallblocks with Volvo drives ran 55 mph.

That is interesting and provocative. Presuming the 8 meter Chris Craft is the 26' (260 model I think it was called) and started with twin 300HPs or 600HP total and now runs the exact same top speed with a single 425HP makes me think that is a good comparison for trying to figure original twins vs modern single in these size older boats. The only question I would have is this. Do the new engines rate the HP differently than the older HP ratings? If the older engines and the new ones are rated the same at the crackshaft, then this might be the start of trying to calculate a formula for switching from older twins to a modern single in terms of expected speeds. Between dropping considerable engine and drive weight in the comparison and having one less drive pushing through the water, this is not at all amazing. However, trying to calculate just how much power it would take to obtain certain speeds with the single would be a little more complicated. Thanks for the input, Bill

[Conquistador_del_mar]

One day .. If I was only a bit more computer literate ... haha

A long time back MP posted a few that I sent to him but a while back I tried to locate them and couldn't .. they were here somewhere ... Maybe he has them stashed somewhere else in his own files and could pull one or two of them again ..

Steve,
I would also like to see some pictures of your Magnum. You might read this thread and see if you can do it yourself. If you still need help, just send me a PM. I think a lot of pictures were lost recently when Scot transferred the site over to a new server. Bill

http://www.donzi.net/forums/showthre...sting+pictures

[Conquistador_del_mar]

There's a Swedish guy on the forum here that re-powered his 27 Sport with a single 496 HO I think?.....and I thought he said it would run about 56-58?

That would be along the lines of what High Life told me. The guy he knows supposedly goes 61MPH with a 415HP package and the one you are talking about with 425HP is almost reaching the same speed - possibly a difference in GPS vs conventional speedo or propping. Bill

[Conquistador_del_mar]

My boat repair friend from here just sent me this listing. I guess I now know what it takes to get to 80MPH in a 27 Magnum single. Would this be originally set up with twins or a race version single since it was raced under the name Double Vision? Check out the diamond plate in the engine compartment. Bill

http://detroit.craigslist.org/boa/841507688.html