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Q1: on a 1995 DAUNTLESS 15 with a Yamaha F70, how can [repeated up-down oscillations of the bow when the boat is on plane] be reduced or eliminated?

The engine mounting height [is two-holes up from lowest position, somewhat more awkwardly described as having the upper mounting bolt in] the third hole down [counting from the top].

The current propeller is a Yamaha propeller [of unspecified material, unspecified number of blades, and unspecified model series] of 13.5 x 16-pitch

ASIDE
I am new to this boat.

The engine running hours are low.

In other threads I read I have not found the answer I am looking for.

[Somewhere] I read that some propellers will lift the stern, and this will reduce [the tendency for the bow to oscillate up and down on plane].

[I have heard some talk that] attaching a [foil appendage to the anti-ventilation plate on the engine sold under the trade name] Doel-Fin is recommended [to suppress the tendency of the bow to oscillate on plane].

Q2: will using a stainless steel propeller [suppress the tendency of the bow to oscillate on plane]?

RandMan wrote:Q1: on a 1995 DAUNTLESS 15 with a Yamaha F70, how can [repeated up-down oscillations of the bow when the boat is on plane] be reduced or eliminated?

A good method to suppress a tendency of the bow to oscillate when the boat is on plane is to:

• adjust the engine trim carefully;
• reduce weight in the transom area; and
• reduce or add weight to the bow, whichever seems to help.

RandMan wrote:Q2: will using a stainless steel propeller [suppress the tendency of the bow to oscillate on plane]?

At the 70-HP power level a steel propeller is not absolutely mandatory, but it generally will improve boat performance. The material of the propeller is probably not a significant influence on whether or not it will tend to reduce bow oscillations. The fact that the steel alloy is stainless and has been buffed and polished to a high shine will not likely affect the tendency for the oscillation of the bow to change.

Propellers using steel or stainless steel tend to be available in more designs than aluminum propellers. The availability of more propeller designs in steel or stainless steel propellers may offer some advantages compared to aluminum propellers in affecting the performance of the boat.

RandMan wrote:The engine running hours are low.

As long as the engine is in good tune, the number of operating hours will not be likely to affect the tendency for the bow to oscillate.

RandMan wrote:[I have heard some talk that] attaching a [foil appendage to the anti-ventilation plate on the engine sold under the trade name] Doel-Fin is recommended [to suppress the tendency of the bow to oscillate on plane].

Use of an extension foil attached to the anti-ventilation plate may seem to help reduce bow oscillation, but it also adds drag and tends to reduce performance. However, some users of them report desirable outcomes.

RandMan wrote:[Somewhere] I read that some propellers will lift the stern, and this will reduce [the tendency for the bow to oscillate up and down on plane].

Propellers with large diameter, large blade area, and little blade rake tend to be “stern lifting” propellers.

On some hulls at certain boat speeds or speed ranges the hull will tend to exhibit oscillation no matter what is done. I see this occurring on my own 24-foot Boston Whaler boat. Above about 40-MPH the hull just likes to bounce the bow, and no change in engine trim other than really a lot of bow-down trim will stop it.