Re-power: 2000 Ventura 18 Now Has Unstoppable Bow Oscillation

[davidB01]

Q1: what changes could help a 2000 VENTURA 18 that was re-powered with a Yamaha F150XD from a Mercury V6 OptiMax to reduce a tendency that has been described by the boat's owner-operator as exhibiting unstoppable bow oscillation when on plane (“porpoising”)?

WHAT IS KNOWN

The new engine appears to be about 80-lbs heavier than the old from online research.

The engine dealer is not a Boston Whaler dealer. The dealer mounted the engine in the top hole. [UNCLEAR--all reference to engine mounting height are in terms of the amount of height in increments of 0.75-inch or "holes" the engine is raised from the lowest possible mounting position. In this case, the engine may be mounted in the lowest possible position.] I don’t know if the “3rd hole down rule” applies to this model.

The boat sits an inch or two lower in the stern and higher in the bow at the dock.

I plan on asking the owner-operator about the current boat set-up:

• What is the current propeller?
• What is the position of the [Anti-Ventilation plate relative to the lowest part of the keel at the transom]
• What is the current engine mounting height?

I plan on checking the following parameters when the boat is underway:

• At what engine speed and what boat speed does the bow oscillation occur?
• What effect do changes in "trim" have on the bow oscillation?
• Where is the [Anti-Ventilation Plate] relative to the water [unclear] when the boat is on plane?
• Does moving my weight (190-lbs) to the bow change the porpoising?

For now I am gathering data to be able to come back to [forum readers] for help and advice.

Q2: What further information should I gather [to allow readers to make a better assessment of the problem and the remedy]

BACKSTORY
My friend has a 2000 Ventura 18 that had the original Mercury 135_HP V6 OptiMax engine, and over the winter was talked into re-powering with a Yamaha F150XD. He said the boat is now porpoising badly no matter how he trims it [while operating in moderate fresh water lake chop. I am going over tomorrow to see it and how it is set up.

WHAT I WILL DO NEXT
Right now I am looking for ideas on what I should look for [on the boat and its new engine and the rigging]. I do not know what I don’t know at this point. I am unfamiliar with the 2000 180 VENTURA

So for now, information gathering for data to be able to come back to you for help diagnose what might be happening and what direction to point him in.

ASIDE
The 2000 VENTURA 18 is not listed in the REFERENCE section.

After research all I could find in various online forums, including searching/reviewing the 400+ posts/replies for Ventura models here on continuousWave and not seeing anything quite on target—but seeing lots on the 210, and lots on the old engine— not much on re-powering this hull with this particular or similar engine). If I missed a thread (or one that is appropriate on a similar model), please feel free to point me in that direction.

[jimh]

A good guide for what information should be included when reporting boat performance is given in an article pinned at the top of the PERFORMANCE forum. See

Template for Reporting Performance Information
https://continuouswave.com/forum/viewto ... f=7&t=9422

Also see

Propeller Testing: What Data to Collect; How to Evaluate that Data
https://continuouswave.com/forum/viewto ... f=7&t=7196

[jimh]

The 2000 VENTURA 18 is not listed in the REFERENCE section.

Yes, that is correct. The principal focus of the historical data in the REFERENCE section is 1958 to 1998. In that 40-year span there is quite a lot of information collected, organized, and available on-line here, but after c.2000 there really is no particularly well organized reference information on the many, many, many models cranked out at Edgewater in the last 26-years. In 2000 the VENTURA was designated as an "18" not as a "180" model.

[jimh]

Regarding the engine mounting height, in order to avoid confusion and to have the simplest, most clearly presented expression of engine mounting height, the website uses a consistent method for describing that mounting height. Please see the article pinned at the top of the PERFORMANCE forum at

Engine Mounting Height Nomenclature
https://continuouswave.com/forum/viewto ... ?f=7&t=739

For some basic elements of engine mounting height and decisions about engine mounting height, see the article pinned at the top of the PERFORMANCE forum at

Considerations in Engine Mounting Height
https://continuouswave.com/forum/viewto ... f=7&t=6618

[davidB01]

Hi Jim

Thank you for the post reply and direction via the referenced articles. I will review before I visit today.

[Jefecinco]

Generally, trimming an engine in, or down, will stop porpoising.

[Masbama]

You can also search for information on a 2000 Dauntless 180. If I’m correct, it has the same hull as the Ventura, including the ‘notch’ in the transom.

[jimh]

In the Boston Whaler catalogue for 2000, the following specifications are listed:

2000 VENTURA 18
LOA: 18-feet 2-inches (5.53-meters)
BEAM: 8-feet (2.43-meters)
DRAFT: 12-inches (0.3-meter)
WEIGHT: 1,950--lbs (884-kg)
MAX WT CAP: 2,700-lns
SWAMPED: 4,000-lbs (1814-kg)
PERSONS CAP: 7
MAX HP: 150-HP
MIN HP: 90-HP
MAX ENG WEIGHT: 510-lbs
SHAFT: 25-inches
FUEL CAP: 65-gallons

[jimh]

You can also search for information on a 2000 Dauntless 180. If I’m correct, it has the same hull as the Ventura, including the ‘notch’ in the transom.

Looking at the specifications in the 2000 catalogue, the 18 DAUNTLESS hull and the 18 VENTURA hull have the same dimensions and ratings.

[davidB01]

Thank you all so far for the comments and suggestions. I met with the owner, and this is what we found

Static measurements/observations
1) The engine is the F150XD 25-inch shaft model. Based on research only, and adjusting for the deleted VRO system, it probably added about 75 lbs to the engine.
2) The prop is the Yamaha SS Reliance Series 15 M 14.5. 3 blade
3) measured the cavitation plate depth relative to the running surface of the tunnel, with the engine trimmed such that the cavitation plate is parallel to the tunnel running surface, Cavitation plate is 6” down. Measured it twice with separate people to verify. Not that it is about 3” down from the lower running surface on the sides of the tunnel. We measured to the surface of the tunnel, as we suspect this was the correct reference point (please verify/correct if not)
4) the engine will trim “down” further than parallel to the tunnel by about some amount. As the boat was in the water, could not figure this out exactly, but the prop came “forward” another few inches.
5) engine mounted in top hole, so all the way down. There was a mark on the bracket at the 3rd hole down (which would be two clear up configuration, or 1.5” further up) indicating maybe the installer had tried there, but there is a small black rubrail across the transom that would have prevented a full contact attachment in that configuration. there are only 4 holes on the mount.
6) the boat does sit about 1.5” lower in the stern and correspondingly higher in the bow based on the water line stain on the boat.

Sea trial. Boat as configured per JimH’s notes above (and noting the hull shape is the same as the 180 Dauntless of that era). Two male adults @ about 190lb each. Fuel tank about half full (so about 32 gal). Used the tach on the boat (no idea if calibrated correctly) and the GPS speedometer app on my phone.

Conditions were moderate wind chop on the lake with about 10 mph winds, with occasional bigger boat wakes

A) Initial Planing. Good pull and planed out at about 3000 rpm and 17 mph. Trimmed all the way down. Boat seemed to “dig” and slap hard in the chop.
B) owner increased speed to about 4000 rpm, which yielded 28 mph. Still very rough ride (which was confirmed as the original observation of the spouse). I did not notice porpoising in this configuration, but did observe that the bow of the boat seemed to “pop” up more than expected when crossing wakes.
C) when owner tried to trim up, bow popped up more intensely and with more frequency, and height of “pop” increased when crossing wakes to the point the owner felt need to slow down. It did not feel comfortable running that way.
D) we tucked behind an island to the calmest water we could find so I could try to observe the cavitation plate. It was smoother, but not smooth. I did not take a picture of the cavitation plate as it was buried too far down to even see it. I noted there was severe spray coming out to both sides from the lower unit.
E) in the smooth(er) water, he opened it up. Got to about 5800 rpm and about 40 mph. He noted this is slower than it was with he old 135 Optimax engine.

One addtional comment. The owner’s wife commented that the boat is distinctly slower and more difficult to get up on plane with this newer engine. This was with 4 people on board with 2 in the rear seats. To get up a plane faster, she moved the two people to the bow, which helped. She also observed that the ride with this engine has deteriorated massively (in her words)

Use of the boat. runabout and water skiing for teenagers. Extreme top end speed not important to this family.

Q3: What does the above data say about this setup and performance to those of you whom know this model?

Q4: On this model, what is the proper height from the cavitation plate to the running surface of the tunnel (if that is the correct reference)?

Q5: If it is supposed to be 0 inches, we are substantially low. Is this the right shaft for this boat? (I believe a read there is a SS version of this engine available)

Q6: If we have to come up, what is the best way to deal with the rubrail? Should it be notched, or maybe a 1/4” flat plate as a standoff. Further, if a bigger vertical adjustment is needed (more than 3 holes further - 2.25”), would a jackplate be advisable in this configuration?

Q7. Any other data/measurements that would help?

thank you all for your help for this owner (and his spouse!)

PS. I have several pictures, but file size is too large. Cannot reduce on this device. If you believe critical, I will process through my main computer and add