Barnacles Effecting Performance?

[gkdawson]

Hi everyone! New to the forum and first post!

Wondered if I could get some help / advice. I recently purchased a 2017 Merry Fisher 695 with a Honda BF150HP engine. Boat is in great condition and the engine had only done 30 hours at the time of purchase!

Took the boat for sea trials and everything seemed to be working fine, however I wasn’t too privy in regards to the performance data for my specific boat and engine at the time! (research I should’ve done beforehand, but we live and learn!)

Upon taking her out on the water multiple times I became curious about the engine revs… I noticed high revs and very little go!

For example, I recently took her up to 4000 RPM’s and was only achieving 10-12 knots. From doing my performance data research for this boat and engine I should be achieving 19 - 20 knots at 4000 RPM’s and cruising comfortably on the plain!

I have since changed the propeller with a brand new one as I suspected the old prop may have had a spun hub, this was due to the old prop blades appearing scuffed / chipped, suggesting that the previous owner had hit the sea bed with it, but this hasn’t resolved the issue… the pitch is correct as well!

This leads me onto my questions! I have had the boat in the water and on a mooring for around 2 months now. A considerable amount of growth has accumulated on the sides of the boat and from reaching underneath I can feel barnacles!

So my questions are:

1) Has anyone had major performance issues as a result of fouling accumulating on the hull? Can a short amount of time / growth on the hull without anti-foul affect performance greatly?

2) What kind of performance are people getting with the same spec or similar spec boat / engine?

I’m hoping this is the issue and that there is nothing else majorly wrong, but thought I’d see if anyone had any similar experiences with this problem and if scrubbing the hull / applying fresh anti-foul resolved the issue!

I am coming from owning a RIB which was taken out of the water after every use so I’m not too knowledgable with fouling issues etc! But on the plus side, I make it back to my mooring without being completely drenched after a days boating!

Appreciate any help / feedback that anyone can give!

[NZL50505]

Sounds highly likely it is simply a growth problem.

In a sailing boat (as I have) a simple layer of slime over the hull can turn 6kts into 5kts even though the growth looks fairly innocent.

And a friend with a large planing launch (motor boat) tells me that after one season of strong growth the same engine revs that gave him 18kts (planing) now only give him 14kts (not planing).

[johannes]

Is there no antifouling at all? In that case it will be completely covered with barnacles after two months in sea water. And yes, it will make a big difference on speed.

[gkdawson]

Sept 16, 2021 5:02:10 GMT NZL50505 said:

Sounds highly likely it is simply a growth problem.

In a sailing boat (as I have) a simple layer of slime over the hull can turn 6kts into 5kts even though the growth looks fairly innocent.

And a friend with a large planing launch (motor boat) tells me that after one season of strong growth the same engine revs that gave him 18kts (planing) now only give him 14kts (not planing).

Thanks for this, I’m hoping that is the case! She’s being hauled out next Thursday and scrubbed / power washed etc! I didn’t realise fouling could effect performance that much!

[gkdawson]

Sept 16, 2021 8:45:33 GMT johannes said:

Is there no antifouling at all? In that case it will be completely covered with barnacles after two months in sea water. And yes, it will make a big difference on speed.

I believe she was anti-foiled at some point, but this can’t have been recent due to the amount of growth etc! I’m sure she performed much better during sea trials but I wasn’t too sure on the performance data at the time!

Fingers crossed she performs better after a good clean up!

[gkdawson]

Just to give an update on this!

Boat was lifted, power washed / scrubbed etc!

Made all the difference!! Most noticeably on my fuel economy! I was shocked how much foul can effect performance!

Ran some performance tests and was achieving 19/20 knots at 4500 RPM. I still think I’m 500 RPM over what I should be when achieving those speeds, but the boat is coming out of the water in a couple weeks, engine will be serviced etc, so hopefully anything else will be identified if there are any engine problems! I’m thinking some new oil, fuel line etc will improve these figures!

[johannes]

Good to hear that scrubbing made a difference! 

I suspect choice of prop and trim will make more difference than engine service. Prop type and pitch can easily make a difference of a few knots.

[Sean M]

I know you already confirmed the issue and I had the same issue. I have a 2016 MF 855, that when I first bought it I dry stored it. It was only used in fresh water and only 50 hours on it so no bottom paint ever. The marina I wanted to move it to had an opening in February so I moved it up there. I wasn't able to get around to painting it until Memorial Day week but when I went to take it around the island to the Marina where I was doing the painting I most definitely noticed a big performance hit. I could barely get it up on a plane and only at 4500+ RPM. Just some gut feel I think I was taking about a 30% hit in performance.

Painting was a pain, in the back and arms and legs. Actually, painting was pretty easy. Sanding and cleaning the hull to prepare for the epoxy primer was the hard part.