How Deep should I go?

Author Message   Kc Savage Member Username: island Post Number: 10 Registered: 07-2009 Posted on Sunday, September 13, 2009 - 11:27 pm:    I am in the process of designing a motor support to convert my houseboat from a single outboard to run a pair of outboards. Mostly for manuverability. So what is the optimum depth to get the best performance?   makomark Senior Member Username: makomark Post Number: 1475 Registered: 09-2008 Posted on Tuesday, September 15, 2009 - 09:56 am:    Best to check your engine owner's manual. Most want the cavitation plate parallel to the keel. Since you are moving them out, probably best to use a strake to match up with the plate. Most engines come in at least two shaft lengths (short and long); you can also use that variable to your advantage.   W D Neal Advanced Member Username: chawk_man Post Number: 217 Registered: 09-2008 Posted on Tuesday, September 15, 2009 - 11:04 am:    Assuming you have a planing hull or semi-planing hull, then if the motor is mounted at the transom, the cavitation plate should be parallel to the bottom point of the keel at the transom. If you are offsetting the motor from the transom, say, with a motor extender, then the rule of thumb I have heard is that the cavitation plate should be elevated 1" for every foot of offset from the transom. If you have a displacement hull, then the cavitation plate should be at or slightly below the bottom most point on the keel.   Kc Savage Member Username: island Post Number: 11 Registered: 07-2009 Posted on Tuesday, September 15, 2009 - 02:20 pm:    Thanks Guys, Great info. That is really going to helpfull. I'm going to call it a semi-planing hull, these 38' River Queens originally came with a pair of V-8 chryslers. With that power it was a planing hull. Someone has removed those and switched to a single 165 I/O that is thrashed. The motor is probably rebuildable but the outdrive needs to be replaced. My goal is to get a pair of used medium HP out-boards mounted off the back on a extended mount. 70 - 125 Hp. Or Tripples, that would look cool. Thanks for the help. Any further input on my refit would be welcome.   W D Neal Advanced Member Username: chawk_man Post Number: 218 Registered: 09-2008 Posted on Tuesday, September 15, 2009 - 04:26 pm:    WOW - that's a lot of horses on the original - likely over 400 hp. To match that, you are going to need two 200 hp outboards, or better. Big bucks. My advice on used motors - don't, unless you really know their history and maintenance. Lot's of folks are fooled into buying older used motors with low hours, believing they are getting a bargain. Typically what has happened is the motor has been setting around unused for long periods. That causes a huge number of problems, from stuck rings to fouled up fuel systems to brittle/broken seals. Two new Honda 225's or Yamaha 250's are going to cost you well over $30,000. But, in the long run, it may be worth it because you will minimize your problems over many years. And, if you're spending those kind of bucks, have the dealer handle all the mounting and adjustments. That way you have recourse if it's not right. Must be one heck of a boat.   Kc Savage Member Username: island Post Number: 13 Registered: 07-2009 Posted on Tuesday, September 15, 2009 - 11:01 pm:    Not in the budget. I'm in Stockton, CA. On the California Delta. There are alot of decent used motors around here. My Goal is to be able to cruse around 10 or 12 knots. Without sucking up too much fuel. I'm decent with a wrench so used doesnt bother me and I used to be a construction welder, so the fabrication should be easy. If I was going to go for power, I would probably go V-drive and V-8's. Easer to repair with the boat in the water.   W D Neal Advanced Member Username: chawk_man Post Number: 220 Registered: 09-2008 Posted on Wednesday, September 16, 2009 - 05:56 am:    Well, okay. Just be careful about what you buy - do a compression test before purchasing. Compression should be very close to even in all cylinders, and within published ranges for the particular engine.   Kc Savage Member Username: island Post Number: 14 Registered: 07-2009 Posted on Wednesday, September 16, 2009 - 10:51 am:    WD, Thank You for the intrest and advise. I am currently checking out a '83 Suzuki 115 2 stroke. The owner is letting me check it out before paying. Nice guy. He wants $500 for the motor, a 16' centurion ski boat that has no seats and a lot of dryrot, and a decent light duty boat trailer. So farr I know the compression is good. I am at least going to have to change the water pump. The lower unit gear oil looked old but normal, no water in it. I am about to check the oil injection system. If ok, i'll fire her up.

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