RF-18/Novi Hull Performance Question

[HeidiG]

So I have a 60hp Tohatsu, and Lenco power trim tabs. When I get beyond 3/4 throttle with the tabs down and motor trimmed up a bit, the bow comes down, but the steering gets squirly and I get major splash over the bow onto the pilot house windows. (which sucks without a windsheild wiper) I just can't seem to get it up on a smooth plane. She rides great at up to 3/4 throttle, and I'm fine with going slow. Just need to know if this is normal performance at higher speeds. Any suggestions would be much appreciated.

 

[harpoon83]

There will be a fine line of keeping the bow down, and keeping it down so much that it digs in and bow steers at speed.

I have 70 hp, on a similar hull to yours, but its just a center console with a T-top. With the T-top I just added trim tabs to get the bow down enough to scoot along.

Without the tabs, the T-top grabbed too much air and the boat would not level out.

What are you getting for speed at 3/4 and full throttle?

 

[BOSBoatMan]

Sounds like the boat is porpoising

Common with these smaller novis

Try getting some weight forward (cheap) or a stern lifting propeller

(Cue the every boat needs trim tabs crowd)

 

[PatriciaLynn]

Pull the tabs up and report back. Tabs should not be fully down at speed.

 

[Cutty]

In the video you posted on the other thread it looks like you have a lot of turbulent water washing up between the transom and the outboard. Perhaps the motor is mounted too low?

 

[PatriciaLynn]

I just watched the video and you definitely are using too much tab. Try to run the boat with them all the way up to get a feel for how the hull responds with no tab. Then only use them as needed to 1. Level the hull athwartship while running at speed or 2. To keep the bow down when running into a head sea in order to reduce pounding.

 

[harpoon83]

Like mentioned above, your video is showing a lot of turbulent water coming up around the motor. It almost looked like it was riding up the motor almost to the seam where the cowling splits.

Its possible that the motor is mounted too low, that turbulent water is a telltale sign of a motor mounted too low.

edit...
I am no outboard expert, but looking back at some of your build photo's I noticed a picture that included the motor in its "down" position.

The picture looks like they lined the "upper" fin of the lower-unit with the bottom of the hull. I am no expert, maybe someone else is...
Shouldn't the lower fin be on the same plane as the bottom of the hull, not the upper-fin?

 

[HeidiG]

There will be a fine line of keeping the bow down, and keeping it down so much that it digs in and bow steers at speed.

I have 70 hp, on a similar hull to yours, but its just a center console with a T-top. With the T-top I just added trim tabs to get the bow down enough to scoot along.

Without the tabs, the T-top grabbed too much air and the boat would not level out.

What are you getting for speed at 3/4 and full throttle

In the video you posted on the other thread it looks like you have a lot of turbulent water washing up between the transom and the outboard. Perhaps the motor is mounted too low?

Agree, that just didn't seem right to me. I hate to sound stupid here, but I just went from a 17' Carolina Skiff to this, it's all new to me. I am going to try it next with tabs up and see how she feels. Also, would a 4 blade prop help?

 

[HeidiG]

Like mentioned above, your video is showing a lot of turbulent water coming up around the motor. It almost looked like it was riding up the motor almost to the seam where the cowling splits.

Its possible that the motor is mounted too low, that turbulent water is a telltale sign of a motor mounted too low.

edit...
I am no outboard expert, but looking back at some of your build photo's I noticed a picture that included the motor in its "down" position.

The picture looks like they lined the "upper" fin of the lower-unit with the bottom of the hull. I am no expert, maybe someone else is...
Shouldn't the lower fin be on the same plane as the bottom of the hull, not the upper-fin?

Interesting! Would love to know that answer to this... Thank you for all your suggestions. I thought that didn't look right also.

 

[PatriciaLynn]

Don't worry about the prop just yet. Let's figure out how to get your boat running properly FIRST, the prop is really just for tuning once everything else is dialed in.

 

[HeidiG]

Don't worry about the prop just yet. Let's figure out how to get your boat running properly FIRST, the prop is really just for tuning once everything else is dialed in.

Thanks for your advise, we plan to take her out again next week and will report back. It's a whole other experience for me, so thanks for understanding.

 

[PatriciaLynn]

Thanks for your advise, we plan to take her out again next week and will report back. It's a whole other experience for me, so thanks for understanding.

No worries, we were all been new to this at one point.

 

[HeidiG]

Interesting! Would love to know that answer to this... Thank you for all your suggestions. I thought that didn't look right also.

This is a photo of the mounting instructions.

 

[harpoon83]

Interesting, is the boat in the water or on the trailer? Can you put a straight edge under the hull and check to see if the measurements are correct?

All that water being pushed up around the motor shouldn't be occurring.

When you trial the boat with the tabs raised, take another video. Maybe the tabs are causing all that turbulent water to be pushed up?

 

[HeidiG]

It looks like the tabs are pushing a lot of the water. I will be able to check it all next week, so will report back. Thanks

 

[dyer 29]

So I have a 60hp Tohatsu, and Lenco power trim tabs. When I get beyond 3/4 throttle with the tabs down and motor trimmed up a bit, the bow comes down, but the steering gets squirly and I get major splash over the bow onto the pilot house windows. (which sucks without a windsheild wiper) I just can't seem to get it up on a smooth plane. She rides great at up to 3/4 throttle, and I'm fine with going slow. Just need to know if this is normal performance at higher speeds. Any suggestions would be much appreciated.

i have seen multi million $$ yachts merritt for one built without wipers at all. rainx is all i ever used on my dyer 29. i ran it 3 times from long island to key west just for pleasure and back and would not leave the dock without applying it. some incredible weather was encountered at times and it worked perfectly shedding sheets of water easily and delivering perfect visiblity at all times.

 

[BOSBoatMan]

Wax works even better and holds up longer.

 

[HeidiG]

No worries, we were all been new to this at one point.

Love your YouTube videos! My husband and I retired a few years ago from raising oysters and littlenecks, it's a great job, miss it. Best of luck.