How fast is your 170? How quick to plane?

[woodNfish]

Hi all,

I had my 170bass up to 43mph on the Merrimack River last week. The water was smooth and I found that by trimming my motor up I could increase my speed from 38mph to 43mph. I'd always trimmed the engine all the way down to get out of the hole before and pretty much left it that way for cruising. My boat has a 2-stroke 75hp engine.

If I have two adults in the boat it can sometimes take me 7 - 15 seconds to get up to plane depending on the weight of my passenger. I weigh 180, and most of the guys I fish with weigh more than me. Alone in the boat I am on plane in about 3 seconds, but I've never paid attention to what speed I need to reach to get to plane and what speed I need to maintain it.

So what kind of performance do you get. I am wondering if a different prop might give me better performance. The prop I have came with the boat and I have no idea what size or pitch it is. It is black just like my Mercury. This is my first power boat and I always assumed the prop came with the engine from the engine manufacturer. I may consider buying a new prop if I can get more performance out of my boat.

woodNfish

[Putershark]

I would try one of these
http://www.propulse.se/english/index.html

till you get the pitch set correct for your hull and loading condations then go to a metal prop (though I really don't see the need) after you find the right combo.

Then install one of these to help get you on a plane faster...

http://www.bobsmachine.com/Products/...stabilizer.cfm

Hope this helps?

Dave

[Fischer53]

I have a 170 CC with a 70 2S Yamaha. Never have done better than 41 mph. I suspect that you have as much top end as you are going to get. Possible couple of mph by going to stainless, but you'll pay big for doing that if you hit anything with it. Got some sort of hydrofin? Faster to plane, but it will cut your top end. I lost about 3 mph.

[woodNfish]

Thanks Fischer53, I think I am not getting all the performance I should if you can do 41 with 70hp. My extra 5hp ought to be worth a bit more than 2mph above that.

I don't have a hydrofin, and I've looked at the propulse props Putershark mentions. I am not sure if 4 blades would give me better performance or not, and I wouldn't consider stainless steel. The propulse props are more expensive than aluminum props, but it may be worthwhile getting one of them. My understanding is that the fourth blade adds to your torqu, but sacrifices some speed. Is that correct?

woodNfish

[Fischer53]

I suspect the 5hp difference is smoke and mirrors. I would be surprised if it makes any real discernable difference. My question is why are you concerned if you get 43 mph or 44 mph? Its not going to make any difference on when you get to a particular place. You have to go tens of miles before the time might add up. Wind, currents and waves are much bigger factors in travel. There certianly no negative effect because you are not running at the very possible fastest speed. Others have also gone down the path of getting the absolute max out of the rigs, but I have never understood it. If you are seriously into 'go fast' there is probably better choices than these rigs.

I have no knowledge of the effects of 4 bladed props.

[woodNfish]

My four-bladed prop comment was directed toward putershark who mentioned the propulse blade in his comment.

My only interest in speed is that a more efficient prop means I will burn less fuel at lower speeds. Some of the guys in my bass club have boats that will do 85mph. I have no interest in going that fast on water. I have to decide if it is worth $200 versus the time it will take to get a return on my investment. I did a little math on the problem:

41mph / 70hp = 0.59 so 0.59 X 75hp = 43.93mph

I know the actual performance curve is not linear, but it looks like I may be getting close to the best I can expect out of my engine.

woodNfish

[Putershark]

Wood,

I venture to say the with the Prop surface area being equal, and at the speeds you are traveling, 4 versus 3 bladed props "might" (for I know of some guys who just fly with 5 bladed props) shave off a knot of top end speed. Here again, how many props can you adjust the pitch on? Drop it back one notch if it is killing you very badly which is pretty easy to do with a Prop Pulse (go view their web page) model.

They do though (4 blades) equate to a much smoother engine (remember you cannot divide a circle equally by 3) and better bite both low end and for cruising performance. Mid range performance to me is much more important at $3.00 plus a gallon fuel than raw top end speed anyway. Your performance though is not linear when it comes to fuel burn rates and engine trim, weight in the hull, water conditions, speed to plane (meaning how fast you punch her to get the hull to plane) all play major factors in range. Come on down some time, and I will take you for a ride in my 190 that has all digital gauges with fuel management and see just how little trim, height, and RPM changes can make a big difference in “real time” fuel burn rates.

Let us not forget though that if you really want raw top end speed (not a Triumph's hull strong suit) then you really need a Stainless Steel prop. The Pro Pulse prop though is both stronger (less flex) and lighter and any aluminum prop so I would consider it a good "middle of the road" choice that is hard to beat for the price point. If nothing and after you get the pitch all dial in, one could always go buy another model of metal prop and store it as a back up unit that will never rust...

Another thing many forget is when it is all said and done and you have had that metal prop on your output shaft for a year or more on your saltwater boat and need to take it off… Just let me know how much fun (or fuel you burned in your torch ) that you had in trying to remove it! Ha-Ha…

I also do not agree with the assumption the all cavitation plates kill top end speed. Now if you have one of those huge plastic models that look like somebody mounted the port wing off of a B52 Bomber onto their lower unit… Then yes, that much lift and drag could do such. So study the various model very closely looking at the the wing design before buying one is my best recomendation.

Engine trim angle though (and many forget such) becomes even more powerful if you have a one of these lift devices mounted on your engine. You do not need to use as much running trim (much less trim period) as before OR you can create a lot more drag. Remember as a kid how your hand went flying up or down when you greatly changed the “angle of attack” when you stuck it out the car window at highway speeds? Now double or in some cases triple that same surface area (like flaps on an aircraft wing) by mounting one of these devices on your lower unit and hopefully you can picture in your mind the possible negative effects from using the same “amount” of trim as you used before it was mounted.

Hope this helps some?
Dave

[woodNfish]

Hey Putershark,

For now I am going to forget the prop. It looks like I'm doing okay on that end although I would like to know what kind of top-end speed other 75hp 17 owners are getting. I have considered the hydrofoils though. Some are pretty small which is probably all I'd need.

For now though, I am just thinking of getting on the water and fishing before it is too darned cold up here! I've been scraping and painting door trim the last week in my spare time. Tonight I hit the water!

woodNfish

[h2ofamily]

WoodNfish,

I went through some of the same questions recently with my 17 Logic. I bought a shop manual and read these posts for info. My boat didn't have a tach when I bought it, so had one installed so I could check rpm at WOT.

The boat has a 2000 Johnson 70hp 2stroke and a SS prop when purchased. There are no markings on the prop for size, but the original prop is a 14" X 17 aluminum. After getting the tach installed I checked rpm at WOT and it was on the high side at 5800 RPM. Target for my engine is supposed to be about 5500. I was doing about 34-35 mph with three in boat and trimmed out as best I could. The SS prop was nicked and dinged from the original owner and I was trying to determine whether to refurb or replace.

We do a lot of slalom skiing with deep water single ski starts. I weigh about 185, so that takes some doing. The engine/prop combo pulls me up pretty well and I didn't want to tinker with a bunch of prop sizes trying to find one better. At the end of the day I decided to refurb the SS prop and I installed one of the fins from Bob's machine as recommended by putershark, htp://www.bobsmachine.com/Products/transom_stabilizer.cfm.
I am very happy with the setup. I didn't know about the propulse prop.

With the fin the hole shot was markedly better, the boat stays on a flat plane at much lower speed (12 - 13 mph), and pulling me up from a deep water start is faster. One thing I didn't notice any improvement in was turning, it still skids just like before and needs some fancy throttle work to turn sharp enough for skiing.

I have not taken it back up to WOT with the refurbed prop yet, but at midrange throttle noticed about a 2 mph increase over previous speed at 4000 rpm, 25 mph v. 23 mph with dinged prop.

All in all, the guys who post here with specific answers to specific questions are pretty good and give good advice. I am a novice and have benefitted from them already. Us novices appreciate you experts sharing your hard earned experience.

Thanks.

[woodNfish]

Hi h2o,

On plane at 12 to 13mph, wow! I had my boat up to 45mph on the Nashua river yesterday evening by playing with the engine trim angle. It was interesting-I got it up to 38mph and just by playing with the trim I could move it up to 43mph so I added some throttle and was able to trim it up to 45mph. I am now satisfied with my prop, which came with the boat, and will have to seriously look into the hydofoil fin.

BTW, putershark, my boat is mostly in fresh water. I can count on the fingers of one hand the number of times I've had it in salt water this year. I wash it down with fresh water after every salt water excursion and run fresh water through the engine for about 10 minutes in my driveway. When I am not in my boat on the water, it is on the trailer in my driveway. I only mention that because I take the prop off at the beginning of each season and grease the shaft. It comes off easily and I have no corrosion on my boat anywhere-just a scum line from the dirty water in the Nashua river that I've never bothered to try and wash off.

woodNfish