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Drive depth, surface drive

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Old 04-17-2012, 10:14 PM
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Default Drive depth, surface drive

I've been looking at either a heat or rage (a rage will probably be better for the mostly lake boating I do) and I just cant grasp why these boats need the drive so deep? people seem to adding spacers and going faster most other hulls add shorties and go faster. I know the newer boats have a higher x that than the older boats. How are other hulls running surfacing drives and these boats seem to need deep drives? is there a hook in the hull? no rocker at all? do they need lots of trim like bajas? I have seen a picture of a rage with a pulse drive did it even work? (likely I will be buying a non step hull) Nordics are hands down the best looking boat in my price range and the hulls seem pretty efficient, plus I want a mcob and that cuts down the options. I'm almost dead set on arneson conversion but I cant find anyone who has it on a Nordic. ( I don't mind the testing and if you piece it together the conversion can be be done for a reasonable price.) Please don't make throttle with left hand and wear a gold chain. (just a joke fountains sure do run hard)
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Old 04-22-2012, 10:15 AM
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Professor,
I will try to keep the answer short, and this is in general specific to the Heat. The reason our boats need a spacer, instead of a shorty, is the factory x dimension differential.
I had a Baja (H2X) and like 99.9% of them, the drive was buried at 16" XD. That was not unusual for the hull, which needs lift, and propellers available in the era.
In the early 2000s, Nordic began running a single step bottom, and raised their X dimensions radically to 18.5/19.25".
They were looking for a more efficient setup, but they didn't do a lot of on the water testing under former owner Orval Summerstedt. Several enterprising owners of these boats who DID actually test our boats with GPS speedos and slip calculators realized we had slip in the 18/20% range.
To reduce slip to a more efficient 12% range, several of us have added a 1" spacer, and began running 5 blade propellers for more submerged blade area, better acelleration,
midrange efficiency, and higher top speed.
The concept of running an Arneson drive is interesting, but you'll be "flying blind" from a database standpoint. Sometimes it is easier to go with known variables......
Regards,
Steve
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Old 04-22-2012, 12:50 PM
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Thanks for the reply. I read about the x dimension change that Nordic did. I have read about every thread that had anything to do with a rage or heat that was 80+ mph boat. On the nordic do you need alot of trim compared to the baja?, Or did the baja require more trim? I can't imagine that these boats have a hook, have you ever put a straight edge on the hull to see if there is any rocker in the design?
I know an arneson will be a fair amount of testing,(thank goodness for bblades prop test program) but I just wanted to see if were even feasible. Thanks for the X numbers I can see that Nordic had the bravo in a semi surfacing X dimension and that's why drive spacers are needed. Surfacing drives have been run on plenty of v hulls and when they work they work well. 5-10 mph faster at the same power sounds good to me. I have found fountains, donzis, and scarab that have used them.
If I buy one it will be out of state for sure. in the past 2 years I have seen 2 Nordics for sell that were anywhere near me. one was an evolution and one was closed bow heat.
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Old 04-22-2012, 02:55 PM
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I am no expert, I have not put a straight edge on my hull, or probed for a hook. But I love information and learning, so I hope your ventures prove fruitful for you and then for me
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Old 04-23-2012, 01:53 PM
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I am a former drag boat racer, and have either had the factory blueprint my hulls or done them myself. I am not a stranger to this or bottom coatings. Yes I did check the bottom of my hull when I purchased it, with a 4' level, from the transom forward. It is perfectly straight on the pad and lift strakes, so I never needed to do anything to it, other than clean up the occaisional ding.
Bajas normally do have some hook, and except for the Hammer and H2X, most of them are lacking for lift.
My Heat runs the best with neutral trim, which is the most efficient set up for handling and top speed. If you need to use positive trim to lift the boat, then you are wasting HP.
I have changed a lot of things to get there (drive height, propellers, tabs, HP), but it is working well now.
There is no perfect X dimension for every hull. It actually changes with the HP level. The higher the HP to weight ratio is, the higher you can go. Even then there is a point of diminishing returns where the boat becomes weight sensitive, planes off poorly, or handles loosely in rough water.
If you end up with a Rage, we have plently of Nordic owners who have theirs' set up very well, and I am sure will share what they have done to get there.
Regards,
Steve

Last edited by Steve Zuckerman; 04-23-2012 at 10:30 PM.
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