Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

[jamesdeanj]

I have a Zodiac Futura Mark 2 HD with a Yamaha 25 2 stroke. Just thought I'd share some speeds for giggles. First let me say I'm 6'1" 235. With just me in the boat on realatively calm water I got it up to 27.7 mph. With each person added it slowed about 2-3 mph. These results are on the ocean in San Carlos, Mexico. Rough waters severly affected the speed of the boat. Data collected from my Rino 530HCx gps. If you are only going to have 1-3 persons in your boat a 25hp is more than enough to get you places at a good speed. I would like to get a 40 in the future because I usually have 3-6 on board.

1 person 25-27 mph
2 person 23-25 mph
3 person 19-22 mph
4 person 16-19 mph
5 person 12-15 mph
6 person 8-11 mph

 

[0976claxton]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

Thanks for the post. I just came across this while researching how fast my mark III HD should be moving. unfortunately, with 2 people (avg weight of 160lbs each) in decent conditions, I've only been getting speeds of 17mph. pretty weak. i'm not sure why i'm not going faster. i have a 2001 yamaha 25HP 4 stroke.

 

[Sea Rider]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

That's pretty slow, with a 3.80 Mt sib, gauge inflated to 3.5 psi and a overall total weight of 250 kilos (sib + engine + 3 gal gasoline + 2 boaters weighting same get on plain flat sea, no wind 39.2 Km/Hr, using a Tohatsu 18 HP, 2T engine. You probably have main & small speedtubes with underinflation issues, engine height not properly adjusted, or with different prop pitch.

Happy Boating

 

[FH alumni]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

My 13'9" mark II with a '08 2 stroke 25hp gets approx the same speeds. 29mph is the speed I had the other day by myself. However, the dolphin fin I have installed cuts down on top end speed.

I am curious if a different prop would make a difference. I also wonder if raising the transom up a few inches would add more speed. (and get less water in the boat!!) It's a short shaft but Zodiac drops the transom 2-3" and the lower plate is very low in the water compared to the bottom of the boat.

But honestly, 30 mph on a boat that size hopping swells is plenty fast. Not often seas will allow that speed safely.

I slightly over inflate my boat. PSI is supposed to be 3.4 but my pump setting is 2 bars ~3.5. Dealer says this won't hurt it as my valves will automatically purge any pressure that is too high. I also learned to re air once you put it into the water. If it's full pressure on land the cold water will compress the air inside and reduce the PSI.

 

[Sea Rider]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

The post stated 17 MPH not 29 MPH ? Maybe a typographic error ?

To obtain the best speed with my actual sib/engine configuration had to raise the transom 2.5 cm more, tail was bit low and had water splashing intrussion issues over transom. Now performing excellent, water stream passes slightly under my small upper plate which is visible at wot, trim angle is adjusted on third hole from transom and weight is properly ballanced towards bow. To be only a 18 horse, it's a fast sib.

A different prop pitch same diameter will make the difference, will need to make a wot test with a tacho to see max rpm for that engine and play with available pitches for more speed, but sacrifying best hole shot for top end speed. Engines are usually factory delivered with medium prop pitches so to play with for different boating applications.

Happy Boating

 

[FH alumni]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

Sea Rider: so raising the motor a couple of inches gave you less splash? I get plenty of speed but I would love to get less splash in the back. I get a lot of water in the boat to the point is sloshes around quite a bit at my feet. I know it's only from splash as I have filled the thing with water and not a single drop leaks out. (that and I can see the water splash over the transom, amazing how fast it adds up)

How did you raise the motor? Screw a board on the transom? Is this secure without fear of losing your motor? give me details!! I am very curious.

Wait.. you said 2 CM?? that's like 1/2 inch, that made enough of a difference?

 

[Sea Rider]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

Hola FH

Yes you are right, had to raise 2.5 centimeters high, the main issue was that my transom came with 38 cm height instead of the needed 40 cm total height. This is because the Tohatsu engine has a square exhaust that was hitting against water flow producing the inside sib splash , now water flow passes perfectly under small upper plate located under exhaust, the difference in speed and performance is outstanding.

If you have water splashes isues, check against what part of the engine is the flowing water hitting against when at near wot (horizontal sib) and then raise engine accordingly. If your engine has a small upper plate, water must pass slight under it. In my case as don't like to do empiric transformations that could lead to an engine loss, had to do the job a bit more professional. When doing this job, must re arrange front & rear engine plates heights to be same as before transom modification. See pics.

PD: Do not confuse (1) engine water splashes and (2) water splashing/swirling on back inner tubes/cones as this is normal on choppy seas. Test in plain flat, no wind waters. if still splashing sideways (2) place triangular splashguards between transom and main tubes sides.

Happy Boating

 

[Sea Rider]

Understanding Engine/Transom Water Splashes

Understanding Engine/Transom Water Splashes

An issue to bear in mind if wanting wot cruising perfection :

The main concern for transom's water spalshing against engine is all about tail shape and transom height, that is, if transom is a bit lower, water flow will start to be smashed against upper portion of the small upper plate, inside the so called trouble area. Pic-1

Pic-2 shows same water flow passing slightly under small upper plate, this is the best position as flow water will be cut by the triangle shaped portion. The best speed and performance is obtained when engine plates are paralell to water flow at wot, mainly by adjusting trim angle hole matching third hole from transmom and distributing pasengers/gear towards sib's middle to bow.

Other issues that will have enough influence on best performance are : tube diameters, transom heights, tubes poorly infalted not reaching stated working pressure, passenger & gear excess. There is a great speed and peformance difference when water flow passe by upper or lower small plate. Seems Tohatsu, Mariner, Mercury, Nissan are more prone to water splashes than other brands because of it's exhaust particular shape.

Happy Boating

 

[NorthernPike]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

My Futura MK III w. 40 hp 2 stroke is maxing at 28-29 mph with just me, 5 gal. fuel and a bit of equipment on board. I've been trying to get more. Raised the motor about 1". No difference but it got the A.V. plate to where its just skimming the surface. I switched props and went up 2" pitch from 12 1/4 X15 to 11 3/4 X17 but haven't tried it yet.

 

[Sea Rider]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

If you have raised the lower big anticav plate to skim the water surface is no good at all, on choppy seas will have cavitation problems with prop spinning at high revs and probably water refrigerating issues as water intakes will be too high. Adjust small upper plate (transom height) to skin the surface when at full plane. It's not a matter of guessing any prop to get max speed, you should perform a wot test with a tacho and then play with prop pitch to get the max rpm assigned to that given engine.

Happy Boating

 

[NorthernPike]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

Then what do you think about this picture and post?

http://continuouswave.com/ubb/Forum4/HTML/004104.html

 

[Sea Rider]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

Yes, that method is used also for racing, raising AP out of water works perfect on lakes, plain flat sea, bigger engines are mostly 20/25" in tail height so quite possible to have refrigeration water intakes lower on tail than short shafts ones. Other issue, has electric trim so no need to balance big boat as you would need to do on inflatables. Have you tried the same with water flow passing slightly under small upper plate ? This is the way to go for best general use, the other one is for topping max speed.

Happy Boating

 

[NorthernPike]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

My old used motor has 3 holes in each side of the AV plate. I guess previous owners had fins installed. I was thinking about putting one on but thought it would be better skimming the surface rather than always submerged and creating drag. I also wanted to see if my speed would increase. Speed doesn't seem to have changed much. Runs good on dead calm sea, but I did get occasional ventilation in rougher stuff. If I put on a foil shaped fin it should effectively enlarge the plate, making less tendency to ventilate. Make sense?

 

[0976claxton]

Re: Yamaha 25 on a Zodiac Futura Mark 2HD / Speeds

Thanks for the post. I just came across this while researching how fast my mark III HD should be moving. unfortunately, with 2 people (avg weight of 160lbs each) in decent conditions, I've only been getting speeds of 17mph. pretty weak. i'm not sure why i'm not going faster. i have a 2001 yamaha 25HP 4 stroke.

As a follow up to my old post, i wanted to re-post a follow up message and state that my motor was a short shaft. this was sold with my zodiac futura mark III when i bought it used from a local boater. i didn't learn until later that the futura requires a longshaft. i have a 40 longshaft now, and i'm working on getting it trimmed out correctly. hope my mistake helps someone else in the future.