Hard steering

[Seaver123]

I have a 1996 Boston Whaler with a Yamaha 100 hp fourstroke. At low speeds it handles and steers great. At high speeds it gets harder to turn the wheel? I keep the motor trimmed down to prevent porpoising. Is this hard steering normal? I have only had the boat since Spring. Thanks

[Bilge Rat]

The hard steering is caused by the motor being trimmed down.
You may need to look at a different prop. Prop design is the key, with your hull it may work better with a stern lifting prop.
Stern lifting, bow lifting, 3 blade or 4 blade all these designs will do different things to the handling.
These design differences are independant of diameter and pitch of the prop.

Look on a Whaler forum for like setups and see what props some are running.
Check out Prop Gods, Ken on there has a lot of data and can help with the porposing issue then you can trim up and the steering will work properly.
Also Marcus at Power Tech Propellers is a great source of information and the make their own props in house.

[Seaver123]

Thanks for the information. I will check it out.

[madharchod]

what sort of steering has it got is it ,teleflex cable or hydraulic steering

[BQUICK]

Also, check your trim tab adjustment.

[Seaver123]

Where do you find the adjustment?

[Seaver123]

Teleflex steering

[Seaver123]

My prop says 23-k. Seems like too much for that motor. Dealership says it should be a 15 pitch as standard. The steering is cable not teleflex. My bad

[TownsendsFJR1300]

Where do you find the adjustment?

The trim tab adjustment shouldn't affect the porpoising effect but when adjusted correctly, counteract the torque of the engine.

The tab is just above the prop, at the rear of the lower unit. Depending on the year, etc, there is either a bolt directly thru the trim tab or atop the lower unit is a rubber plug. Remove that plug and they'll be a bolt that you loosen and adjust the trim tab.

On my F150, the tab is set (per the manual) one notch to the right (approx 1:00pm position) when looking from the back with the motor trimmed all the way up.

[Bilge Rat]

The trim tab counteracts engine torque transferring to the steering.
If the steering turns one direction easy and the opposite direction is very hard then adjust the tab. First make sure the steering is not binding. None of this is the OPs main issue.

The prop, a 23 pitch sounds like too much. What is your WOT RPM?

IF you are extremely over propped this will add to the porposing issue. The motor is lugging which is very bad for it. With this condition the motor/prop can not hold the bow up. It will be worse in the midrange RPMs.

Get your WOT RPMs and that will tell you what to do first to correct your issues.

[Seaver123]

My WOT range is approximately 5200. What would you recommend for pitch? Dealers are recommending 15". I can't find anywhere what the standard prop for this motor is. I need prop pitch and dimensions. Any info is appreciated.

[Bilge Rat]

What is the max rpm for the motor? It will be in the manual.
As a guess the max may be around 6000.
5200 is a little low but a 15 pitch is not right either.
There is no standard prop, you select a prop based on the WOT RPM of THAT motor on THAT boat loaded the way YOU normally run it.

If the max. rpm is 6000 and you are turning 5200 you are 800rpm low.
1" of pitch change = 200rpm change generally.
Based on 6000rpm max you may need a 18 or 19" pitch.

Are you trimming up the motor to get 5200? If not you may not need as much pitch change.
A prop that gets you very near max rpm will help your issue and trimming up some will make the steering easier.

If you need a different pitch prop one with more overall lift or more sternlifting prop. This will tend to make the hull run flatter so you can run with some trim without the porposing. Most flatter bottomed boats don't need a bowlifting prop which makes it act like a skipping rock.
A bowlifting prop lifts the bow by pushing the stern down. By trimming all the way down the motor is slightly pushing the stern up. The motor is fighting the prop design.
Hull design, motor torque and rpm, and prop pitch and design need to be balanced for good overall performance.

There is no magic prop, I have 5 props laying around. All have good points but 2 give me what i want.

Get the boat handling good at the speeds you normally operate at.
Forget about max speed if you are not racing. A good handling boat is the goal and the prop that does that will usually be only 1 to 3 mph slower than a go fast speed only prop.

I deal with flats/inshore boats that are prone to porpoise in the midrange when not propped right.

[Seaver123]

Thanks for that information. I guess I will have to experiment.

[BQUICK]

I would trim up to where it just starts to gently porpoise then trim down a little until it stops. You will be running at best efficiency at that point and it will reduce steering effort compared to trimmed all the way down (if that's the way you have it now).

[Seaver123]

Ok thanks. I also just ordered a 17" pitch prop. Will see if that helps as well.