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Engine Height and prop for 70HP 4 stroke Yamaha
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| Metalcaster |
Posted on 09/15/11 - 6:25 PM
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I have a 69 Katama that is going to get a new 70 hp 4 stroke Yamaha put on it next week. How many holes up do you think would be the best mounting height? Also, what size prop do you think would be best for good overall performance?
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| Tom W Clark |
Posted on 09/15/11 - 7:28 PM
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I suggest you mount it three holes up and use a 13-1/4" x 15" Stiletto Advantage 4.25.
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| tedious |
Posted on 09/16/11 - 4:57 AM
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Tom, I use that prop on my 15 with the F70, and it's about right. I wonder if it might be too much for a Katama, particularly if it is carrying a lot of gear or water weight?
Tim
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| Tom W Clark |
Posted on 09/16/11 - 6:38 AM
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Perhaps, but I don't see where Metalcaster says he has a waterlogged hull and carries a heavy load.
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| tedious |
Posted on 09/16/11 - 10:24 AM
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As far as I can see the 17' hull generally takes about 2" lower pitch than the 15', so based on the 15-pitch being about right for my 15 with that same motor, I'd think the 13-pitch Stiletto might be a better choice. I actually use a 13-pitch on my 15 for watersports and other heavy loads and it works fine.
Tim
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| Tom W Clark |
Posted on 09/16/11 - 11:24 AM
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You may be right. I would be best (as always) if some propeller testing could be done before a purchase is made. If Metalcaster can try both the 13" and the 15" Stiletto Advantage, that would be ideal.
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| Metalcaster |
Posted on 09/16/11 - 1:01 PM
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I will have a significant amount of extra weight in the boat. It started as a Katama and was converted to side console. It has a homemade plywood front deck. I will be using three 125 amp hour batteries, a bait tank that will have up to 40 gallons of water, and 2 anchors. Fuel will normally be 12 gallons or less but I may take more when I go saltwater fishing. Normally only myself and some times one other person will be onboard. The boat doesn't seem to have much if any water in it. I plan to get an aluminum prop. I just don't think the extra $100 plus dollars is worth it for me to get stainless. I appreciate the advice that you guys give. It will be interesting to see how it runs with that lightweight 4 stroke 70 on it.
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| John Fyke |
Posted on 09/16/11 - 1:08 PM
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The senario will change with an aluminum prop. Tom will chime in on this.
John Fyke
Re-Fit or Reef It
1979 15' Sport with Super Sport conversion and 70hp mercury. |
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| Tom W Clark |
Posted on 09/16/11 - 2:33 PM
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When asking for propeller advice it is important to describe the boat you have. You said you have a Katama but it turns out you have a modified 16'-7" Whaler. What it started life as is now irrelevant.
The added weight is OF COURSE going to have a profound effect on performance and the choice of propeller. It is best to mention that up front.
Yes, I agree that if the boat is as loaded as described, the 13-1/4" x 13" Stiletto Advantage would be the better choice.
I would not waste money on an aluminum prop; it will cost more in the long run because you will burn more fuel and it will not last as long.
I find it very hard to believe an extra $100 is not possible if you are spending $7000-$8000 to have brand new Yamaha F70 rigged on your Whaler. That is ridiculous.
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| Metalcaster |
Posted on 09/16/11 - 5:37 PM
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I don't know much at all about props. Most of the discussions about props that I've heard or read was about a small difference in top end speed or holeshot difference. I didn't think about a difference in fuel efficiency. Prop performance hasn't been much of an issue for me in the past. I only have a 20 hp motor on the boat that I used for the last 20 years. The reason I was thinking aluminum prop is original cost plus one rework would be cheaper than a stainless prop. If you're talking about much of a difference in fuel efficiency between aluminum and stainless props, I think the stainless might be the better choice. It's always good to check out the options before making a decision. Would you get same size whether it's aluminum or stainless? I do a lot of night fishing and often hit wood floating or sunk just enough to hit the motor skeg. Would that influence your choice of aluminum or stainless? I can spend the extra money to get stainless. I just don't like the thought of hitting debris and damaging a stainless prop. Obviously, I'm not familiar with how much punishment a stainless prop can take without being damaged. Like to hear everybody's opinions.
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| tedious |
Posted on 09/16/11 - 6:11 PM
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Get the stainless 13-pitch direct from Tom, or from Dan's Discount Props. It'll run you about $220 with the hub kit, which is likely to be very little more than what you'll pay at the dealer for aluminum. Your new stainless prop will survive encounters with pretty much everything except rocks - you won't lose a blade to a waterlogged 2x4 like you would with aluminum.
Honest, it's not worth fooling with anything but stainless. Install it and forget about it.
Tim
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| John Fyke |
Posted on 09/16/11 - 6:40 PM
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Tom always quotes stainless in size. I think he made it very clear he would never go aluminum and neither would I.
John Fyke
Re-Fit or Reef It
1979 15' Sport with Super Sport conversion and 70hp mercury. |
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