Mostly retired spend all my time working on or thinking about boats and outboard motors :)
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Follow our project from start to finish

 

Power Options

Our particular design was picked, not only because the basic structure of the boat would suit all our needs, with some minor modifications (more on this later), but also because the designer made allowances for different power options.

Single or Twin Outboards, Inboard/Outboard (I/O) Sterndrive or Inboard V-Drives were all viable for this particular design. The designer suggested a minimum of 90 horsepower and maximum of about 300 horsepower for this particular boat.

So what to use? We read about diesel and gas inboards, inboard/outboards, outboards. Used resources such as boattest.com to compare performance reports, fuel per hour consumption etc.

After chucking major dollars at a project that could take hundreds of hours to complete, you don't want to end up with something that you can not afford to run. At the time that I'm writing this, gas has just fallen from summertime high of over $5 a gallon back to under $3.

Given that, you need to determine first "how much power do I need?" and "how much power do I want?". They are not the same thing. You might be able to rig a boat to clock out at 70 mph, but do you want to spend 200 dollars an hour in fuel to accomplish that?

I'll wander a bit here which will help understand our ultimate power choice for this build. I am the son of a diesel/small engine mechanic. I grew up around motors and although I never followed in his career footsteps, I have been working on all kinds of motors since I was old enough to hold a screwdriver. I took a particular interest in outboard motors (more fun than lawnmowers or whipper-snippers when you are 12 years old) and that has stayed with me over the years.

I now run a (very) part-time business out of my garage repairing outboards and rigging powerboats which I plan to turn into my part-time/full-time business in the next couple of years. I also spend numerous hours as a senior writer on marineengine.com giving free forum advice to others trying to do rigging and repairs themselves.

So, back to the choices. Using some specialized marine software that I have, I determined that I would require 135-150 horsepower to get a top end speed of about 30 mph out of this rig and that a decent cruise speed of approx 22 mph could be easily obtained burning approximately 6 gallons per hour (with a gasoline engine) - again, reasonable for this size of boat.

After first reading all the pro/cons about diesel engines, it sounded quite promising. Yes, diesel is a little more expensive than gas, but a marine diesel can get up to double the "gas mileage" of its gas counterpart - sounds like the way to go, right?
Well, yes and no. A marine diesel works best on an offshore cruiser. It likes to be started and run for hours. In fact, they tend to last better if you "drive the snot out of them". Perfect if you plan on cruising from Nova Scotia to the Bahamas on a regular basis, not so good if you are a "weekend warrior".

Then the cost comes in. A gas inboard/sterndrive (motor portion only) producing 220 horses may set you back 5K. Its diesel counterpart goes for almost triple that. So in the end, you have to really really use it a lot before the cost savings in fuel accounts for the added initial cost to purchase. If you put less than 2000 hours on your motor a year, then diesel is probably not a good choice for you (or me either) :)

So that was decided - gas power. Now, which way to go. The two choices I was comfortable with was either Outboard or I/O Sterndrive. If you are fitting "new" motor(s) there are pro's/con's to both.

There are numerous reputable marine engine dealers located in/around the Great Lakes where I live. I could install a brand new Mercruiser or Volvo gas Sterndrive in the 180 horse class, including the drive and all other necessary components for under 8k. Not bad. That would give us a "finished boat" for less than 40K.

Compare the Sterndrive to an outboard of say 150-200 horsepower, that regardless of mfg has a price tag of somewhere around 15k and the former looks like a viable option especially if "price" is a major factor.

I am far more familiar with maintaining/fixing outboards and maintenance and repair is a long-term cost factor. While I do have sufficient resources and skill to work on a Stern-drive, the idea of bent over working down below decks on a motor is not appealing. But that's a personal choice.

So, we opted to go with a single outboard for the main power and a "kicker" outboard for trolling and "in case of emergency". The main motor would be in the 135-150 horse range and the kicker perhaps a 8 or 9.9 horse.

I'm of the opinion that you should never leave the dock in anything larger than a canoe unless it has 2 motors. Ya, it costs extra for the redundancy, but I've never had to paddle home when the main engine conked out - and yes, despite my particular skill in that area I have had main engine failures - they can and do happen - if you boat long enough and often enough they WILL happen to you.

Selecting a single outboard (with a kicker) as the power source will affect our build and needs to be accounted for. The designer allows for up to 1300 pounds of motor/drive in the stern of the boat.
Since "our" combination will come in a little under 500 pounds, this could potentially lead to a bit of "unbalance". We will have to be careful and re-evaluate the placement of some items/components to try and maintain the proper balance on the finished boat. Too much weight forward could cause the boat to "plow" water. So this will require a bit of thinking in the initial planning stage. However, we also have to consider that at some future date we may want to run twin outboards which could add more weight to the stern – you don’t want to totally limit your options.
 
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