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Old 08-18-2017, 02:20 PM   #1
mcalister.eric
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Starcraft 18' aluminum outboard

Hey guys. Im trying to get some help on re-powering my 18' aluminum center console. I got this boat cheap and ran the 1970 mercury 80hp motor for the season. Time to replace it with something a little newer. I was hoping to get some suggestions.
It my first boat and am learning a lot. Everything on the boat is new(electrical wires, fuel lines, fuse panels switches, u name it).
I currently have a 80 hp 2 stroke motor that powers the boat nicely. I have buddys say that a 50 hp 4 stroke would be comparable. Can some one verify this for me. The more research i do the more confused i get. Between hole shot, weight to power, etc... if anyone has a setup close to this and could give me some feed back that would be great. Boat is nothing special but it great for with i use it for. Thanks in advance

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Old 08-19-2017, 11:30 AM   #2
Wood Guy
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Re: Starcraft 18' aluminum outboard

Nice clean looking rig!
I would guess, and that's what it is without weight and what your performance expectations are, but a 70-75 hp new 4 stroke might be closer to the performance you currently have, or maybe a little better. Hole shot can be adjusted with prop choice, but a smaller engine like a 50 hp will require more rpm's for the same speed, and if it requires cruising at 4500 rpm's to get the same speed as a 70 hp at 3500 rpm's, the fuel economy of the smaller engine will be significantly worse. A 50 hp might get the boat on plane, but I doubt that the performance would be the same as the old 80 hp. I get that it's a newer engine and all that, but I don't think a new motor would be 60% better.

Years ago a friend had a 85 hp Johnson, and I had a 115 hp Johnson on exactly the same model boat. When we fished together my boat's performance was significantly better, which was no surprise, but the fuel economy was also better since I was cruising at 3500 rpm while he had to cruise at 4500 rpm to match the same performance. An unscientific comparison for sure, but I thing still worth considering.

If you go to a reputable dealer, know the weight of the boat, and know what you want for performance, he should be able to size the motor and prop right. If you haven't already, you can also do on-line searches for a boat of your style and weight, and get a pretty good idea of expected performance with various motors. These days, weights for specific motors seem to vary mostly from different block designs, ie. 3 or 4 cylinders for the same hp motors, and might be surprisingly close to what you are taking off the boat, although they will look huge.
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Old 08-20-2017, 01:00 AM   #3
mcalister.eric
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Re: Starcraft 18' aluminum outboard

Thanks for the response2 wood guy. That's just what i was looking for. Clears things up a little more for me. I have been digging around on boating forums and couldnt come up with a good answer besides everything that isnt theirs is wrong and sucks. Lol. I dont mind going 2 stroke again but just passed up a suzuki 50hp 4 stroke because i feel it would be underpowered like you stated.

I guess i need to be patient bc there is nothing used in the san diego area at the moment.
If anyone knows of a used 2 or 4 stroke in the 90 to 115 range id be interesed in looking at it.


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Old 08-20-2017, 08:52 AM   #4
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Re: Starcraft 18' aluminum outboard

You've probably already checked this, but what's the max rated hp for the boat? It's on a metal plate that also gives the max load in Lbs and # passengers. I've always found that, as an approximation, one hp size under the max works pretty well for a combination of power for water sports and economy. So, if the boat's rated for a 115 max, a 90 or so would work perfectly, but a 115 would also work well. A 50 might be mounted on the boat in the showroom, but that's all about keeping the purchase price down, and the performance would suck unless you were using it for lightly loaded fishing or cruising.

If you're shopping for a used motor, be patient, and look at all the motors you have time for, including the ones on Craigslist. That way, you will know that "deal" when you find it, and won't lose it while you're researching the motor/ price. Best choice would be motor on a boat. Insist on a test ride as a contingency to closing the deal. Ride should include starting cold, if at all possible, and running wide open for 5 minutes at a minimum. Neither can be replicated in the driveway, and lot's of motors start and sound good in the driveway with no load or back pressure from the water column. You'll want to see a strong stream of water from the weep hole, and smooth shifting. Also, check the compression. All cylinders should be at or over 110 psi, and be within 10% from highest to lowest.

Don't forget the remote shift/ throttle/gauges. If the model year or brand is different, your remote/ cables might not fit the motor you just bought, adding a significant unexpected cost. If the seller is getting a new motor, he probably will need new remote and cables anyway, so is usually willing to make them part of the deal. Lots of times you can get the tach, temp, trim, etc. gauges because the new motor will have a smart gauge that has all that stuff already in the cable coming from the motor to the smart gauge. The stuff I mentioned can add $500 or more to the motor if bought new, but if the seller can't use it you can usually get it at a fraction of or even no additional cost.

Last edited by Wood Guy; 08-20-2017 at 09:16 AM.
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