Magnum 35 questions
 

Hello all,

I am the new owner of a 1972 Magnum 35. The sale was completed through a boat wholesaler and I was not able to speak with the previous owner. The boat has been on the hard for two years and this sale was as-is where is, with no sea trial possible. It has had major upgrades recently completed including newer 2006 Fuel injected Captain's Choice 502ci Crusaders. I believe they put out 385 hp each. The listing stated that my boat weighs about 16,000 lbs. Since these engines are mounted far aft and utilize v-drives to transfer the power out to the props, I am concerned that the boat may be stern heavy and underpowered. Can anyone out there give me an idea what the cruising speed might be at 3000 rpms? Other than this forum, is there any other website that may offer more information or details about this boat.

Thanks
Rich

Did you ask Magnum Marine?

No way it weighs 16k. Probably 10-12k.

Most likely will run about 60mph at WOT with that power and around 30 mph at 3000 rpms.

All above is just guestimates.

My Magnum 38 was also equipped with gas engines, 454's and vee drives. If anything the boat was too light in the stern as the design was for diesel power and the gas engines were quite a bit lighter.

Probably the best speeds I saw were in the mid 50's at WOT.....but then again it went through anything the ocean could kick up.

Great boats, Congratulations and enjoy it.

Charlie M

More like mid 40s MPH top speed and 25 MPH cruise. Weight is probably close, 14-16K. They are tanks.

Thanks for the responses. I did leave a message at the Magnum website. My boat is actually still listed on the Magnum used boat brokerage, as well as Yachtworld. It's listed as a 35 Express. Hull is blue and the name is Pelican if anyone is interested. I have read all of your responses and am inclined to agree with murfman. The boat is a tank, solid glass, and quite beamy. I don't see see 60mph. If it performs at 40 wot, I will be very happy. Am hoping for cloder to a 30 knot cruise as opposed to 25. Very disappointing that I have no history or paperwork. Even the engines surprise me at 385 hp. These are 8.1 liter fuel injected motors. I would have expected 450-500hp, especially from Captains Choice Crusaders. I had a pair in another boat (35 Tiara) that were 500hp with fuel injection. Even though it had all that horsepower, the boat was a pig and wouldn't move unless the rpms were around 3800. That's why I am a little nervous about my Magnum. Rich

Several were used as raceboats--late 60's early 70's---the 12' beam was an asset---


http://i68.tinypic.com/2zgs1tc.jpg

An asset to the oil companies!!
Funny how what used to take six engines, you can now do with two big Verados!

What horsepower rating were each of the outboards shown in this photo? Can't tell if they are 100 or 150s.

Rich

From memory the red band straight sixes came out in 100 then later 125 and 135 (in Australia). I think the U.S. was the same.
There's probably only about six of them left in the world if you're planning the same setup! Lol.

Outboards would be interesting but I think you've got a big heavy boat to move and conventional inboard/sterndrive is still the better option.

RR



EDIT. Zooming in, the one on the starboard side looks like a 135...

The Super BP, was 100 cu. in. and 140 HP---

http://i66.tinypic.com/b3x4ja.jpg

If they are 135s, that totals 810 hp. My twin Crusaders are 770 hp, not much less. I am sure the race boat was lightened up quite a bit, but maybe I will be pleasantly surprised next Spring.

I think you will find that the motors will be more efficient at 3500 rpm in that boat with the fuel injection. That may give you a cruise closer to 30MPH.

I would think the 502ci is a big torquey motor. Is it bad for them to run consistently at that high an rpm? I bet they are a lot thirstier at that speed too:-)

I found an original sales brochure on eBay for a 1969 35ft and it stated that the boat came standard with 325hp inboards. It also stated that it was the fastest 35 footer available. In those days though, 20-25 knots was fast for this big a boat.

Back in the days when all V-8's had carbies, the economy was ok up to about 3200 rpm but above that, the secondaries opened up and they started drinking heavily. Fuel injection has helped reduce that thirst surge in the mid range.

I agree with Katanna, you might see the hull running more efficiently with a bit more speed and leveled out. Load on the engines might be slightly less at 3500 rpm with the boat running nicely.

If you're leaving it in the water, a clean bottom is essential. Dirty bottom can cost you 5 mph easily and worst case scenario, you wouldn't even get on the plane!

Cool old boat, I'm sure you'll enjoy her.

RR

Thanks for the info. The boat is really in great shape. Hull was completely redone in 2008 with new barrier coated bottom, new topside paint, and all new running gear with the exception of the vee drives. The foredeck is rock solid. The teak cockpit decks are a full 3/4 inch thick (imagine that) and need a good refinish to get years of varnish off, but are in great shape. The only thing I am a bit dissappointed in is the aluminum framed windshield. That is going to need attention. Maybe Awlgrip it white. Would have been great if it was stainless. I did find some old paperwork in the boat. Appears that it was on Lake Michigan for much of it's life. That would explain why it has held up so well over the years.

Nice looking boat (stole a few of the photos from Yachtworld) but with antifoul and the V-drive shaft angle in a heavy boat, I think 40 mph would be a little optimistic. Keep that bottom as clean as you can.

RR

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Work out the prop pitch, rpm, ratio.

Isn't it reasonable to assume that the prop pitch/rpm ratio would have been correctly done at the time of the repower? What is the general rule of thumb for engine rpm at wide open throttle under full prop load?

Put me in the pool for a 38MPH top end, 24MPH at 3000 RPM.

Look around on the Crusader site for your engine's data sheet. I believe the max recommended speed for that engine is 4600.
So as Brownie said you will need to find the gear ratio of your v-drives then run the numbers and you'll have your theoretical top speed. I'm not sure what is typical for slip ratio on those props.

Magnum 35 side fact, The 35 Apache uses a Magnum hull. Bob Saccenti didn't even know it at the time. Thanks for that one Brownie. Read all about it,

http://www.***************.com/brown...es-like-topsy/

I had no idea they were 12' wide. I guess 16k is possible then and speeds are probably more like 50 max at WOT.

I think Ghost has it right or at least very close. Back in the early/mid 70's when Magnum was an Apeco company I knew the then president of the marine division. He had a 35 in Burnham Harbor in Chicago. I kind of remember it running in the mid/high 30's. He then got a 38' flybridge with a pair of 482's. I think that one was a bit faster and did reach 38.

Griff, I think they weighed even more than that. And I don't remember any of them getting close to 50. Think "floating Sherman tank"

Yes, HP will dictate the limit of top speed. Getting the pitch/gears right will allow making use of that HP to reach the limit. (AKA: "you can't work magic, all you can do is exploit your HP well. Or you can get it wrong and waste more of it").

Inboards are so much less efficient than sterndrives that I think many of us would naturally overestimate speed of a Magnum 35. Also, it's heavy and beamy, as has been said. Perhaps a not-unreasonable comparison might be a 35' Tiara. I think one of those would reach 33-36 mph with twin 8.1 Crusaders. I guessed 38 based on some rough calculations in my head based on a few memories/boats.

But as a data point to consider, my Nova Marine 24 just reached 50mph, with twin v-drive inboards and fresh 300HP small blocks, at 8'3" wide and closer to 5000 lbs. That was with the gearing and pitch set up right. (With the gearing very wrong, it would reach about 46.) It was a great beast and it felt like it'd go through anything. The 35 must feel like that plus a whole lot more.

I'm hopeful for 38 for this Magnum but honestly, that was at the high end of my SWAG range. I wouldn't be totally shocked if it were as low as 33. Such a cool boat--I've always wanted one. I wonder what one would do with, say, a pair of Konrad sterndrives or XRs and maybe 500-600 HP/side. I'm sure it would like the efficiency gains. I have no idea if it would completely throw off the COG and screw up the boat. But if it did well (and one had a BIG lift to keep the running gear out of the water) it feels like it might be pretty cool.

(With apologies to AB, as I have heard some references to his view of sterndrives. Something like "spawn of the Devil" comes to mind. :) )

Another consideration, depending on your budget, would be conversion to Arneson drives. They are expensive but Magnum has done many conversions to these on their v-drive and straight inboard boats. They claimed as much as 15% increase in speed and fuel efficiency. Some do come up for sale occasionally on Offshore Only. It would make the most of what horsepower you have.
If you ever re-power go for cubic inches. Higher torque motors always help.

Good luck!

I was going to mention Arnesons too but you beat me to it. Years ago a friend had one of these that he converted to Arnesons and diesels I believe but I can't remember details on the motors. It did run much better with that combo but that was pre gps. Sorry not much help...
Pretty boat, I'm right across the Sound from you more or less.

My brother has a 28' Donzi Sportsman that is a 28' x 101/2' beam with twin 454 Crusader engines & vee drives, it's a heavy hull around 13k that runs 45mph on a good day. The 35' Magnum looks to be a enlarged version so it must way in around 16k, performance 40mph ??. From the 35' Magnums I have seen diesel power would be a better choice for weight distribution as the 35' Magnums ride high in the transom with gas power..

using the zoom in button i see the "ghoul" direct from prama ohio in the right corner ...hmmmmmm

Nice boat. I like those.

I own a 1970 35 Express very similar to Pelican. In fact I contacted the broker for Pelican while I was researching prices. My boat has mismatched engines (502 port, 496 starboard). I find that at 3000 rpm it settles in about 20 knots. In fact the formula RPM/100 minus 10 yields pretty accurate speeds (ie 15 knots at 2500, 18 knots at 2800, and so on). At WOT the 496 stops at about 3800 rpm indicating that its overprop'd. It should go to about 4600 at WOT and max continuous cruise at 3800. The 502 still has alot to give, but the boat starts to list and I have to put in alot of rudder to counter the yaw so I've never gotten to WOT on it. The previous owner swore he saw 39.7 knots on the gps once.

It's a tank, but really smooth and comfortable in the bigger swells.