You could be right. The only other things I could think of would be a worn prop bush or weed around the prop causing cavitation. Interested in other peoples thoughts.

 Could be something around the prop or affecting the motor. A similar thing happened to us and 3hrs later back at the ramp we realised the earmuffs were still on 

 A 475 with a 40 is definately going to require your load to be well distributed to perform. 

Give it a try next time with the same weight. Get her on the plane then redistribute the weight up to the front. I bet she still planes well. That will show that she was just pushing the water in front of her an unable to get on the plane - on your first trip out last weekend.

agree with the all comments above,
that size boat with a 40 is always going to be a bit underpowered imho especially if you are taking that load out
so first up , if you cant repower it with something bigger over time , then really check all the stuff that you & your mates are putting on board is really needed ?? often we just chuck shite in without really looking at what it weighs ? tackle boxes especialy may not all be needed , just a few selected items will often do what you need , or share

amazing how many blokes have tackle boxes full to the brim of stuff they take and only about 10% gets used on any one trip ,

its all extra kilos in the hull

second , distribute the weight of what you do put in evenly ,

hezzy

 Yep, I've stremlined the amount of gear I take out now, a very light tackle bag with the basics and one small box with pliers, brag mat leader etc and a very small weight box. I have under floor kill tanks which frees up the deck space too. You could do the Lambada on my deck while fishing lol.

had 2 stroke 150 now 4 stroke 200  most ill ever do is 4,200 revs .

 Hey Stevee, I'm actually doing a bayhunter up at the moment and have brought a 60hp 4 stroke Suzuki for it. I did a fair bit of homework on this before my decision so I think yeah you may be a little under poewered. If you are planning on keeping the boat for a while might be an idea to upsize?

Yea definitely hearing the comments about loaded tackles boxes which don't get opened!... Would love to put the max hp on the back which is a 60 but as always it's a matter of $. Surprisingly it's actually a lot better than you would think with the 40. 

Thanks for the comments, think I might go out of my way to experiment with it next time I've got 3 or 4 on board. 

 All bandaid reasons and solutions.

You need a bigger boat  

Hey think all here are right that the boat is slightly underpowered but if the boat normally does 20kts at WOT and only got to 7/8 kts before stopping and redistributing load my guess is that you had weed around the prop.

have had it happen to me going out of the woodies entrance ...you just get a "muffled rev" but no power

happenes all the time even to bigger boats. most just put it in reverse give it a rev and get underway again.

 I used to have a bayhunter with a 40 2 smoker and I think what you will find is your overloaded for the boat.  Mine was licences for 5 people @ 75kg and that's without any gear in it.

i could hit 24knots with a deckie and fishing gear but put 5 people in it and it struggled in the river

i fitted a hydrofoil to mine and it made a noticinle improvement but at the end of the day your probably pushing it a bit harder than it was designed for 

you might want to think about setting some limits on your load depending on where your fishing &conditions

for me id only want to take out one crew if i was fishing off the coast , in the river maybe more

but at sea /wind conditions can change quickly, being at max load gives you bugger all options in the event of any changes

hezzy

I was definitely conscious about not heading too far with how it was performing. Hence why we stopped quite close in. But as i said, after the first stop it was like a different boat. Happy to get on the plane and perform. And we still had the same amount of weight on board apart from maybe 10 - 20l of fuel which was burnt throughout the day.

Just to clarify there was 3 people total on board. Myself and two others. I have had four on board in rivers/estuaries with two up the front and 2 on the rear bench seat and didn't have the same experience as on saturday. I think next time i have four on in an estuary ill experiment and see if i can replicate what happened. 

Originally convinved it was a distribution issues with a slightly underpowered motor pushing into a greater frontal water resistance. Now I think because it got better so suddenly you had a weed issue that cleared when you stopped.

 Agree with a lot of the above. Also, what prop do you have? At 5500 max rpm it may be just a touch to low rpm wise. It's worth checking out the WOT rpm range as that sounds like it's just slightly on the bottom part of where it should be. It does sound like you need to get the balance right for that set up. 

 Yep still the same motor as per profile...

Will have 4 total on board tomorrow in the river so will experiment and see how I go. 

Cheers for the input so far guys

I wouldn't have thought  you would get normal wot rpm if you couldn't get on the plane? not at least without some cavitation. If you had weed or something wrapped around the prop I would Have thought it would lower your rpm, unless your rubber bush in the prop is damaged causing your normal revs? I could be way off the mark here  idk but worth a thought...

I have a 4.5m  with a 40hp 4stroke merc tiller steer no infloor tank and is perfect with 2 adults, but adding one more in the front does affect how I have to load the boat.

Hmmmm well today was interesting.... I'm starting to lean down the path of either cavitation or a spinning prop hub...

I Launched at maylands and went through the ski area at WOT for 7-8 knots!! So throughout the day I was playing with slight trim adjustments and rpm increases and noticed that it loads up toward 4300 - 4500 rpm, a couple of times I left it at that rpm (trim needed to be exact) and id get a vibration through the hull but eventually we'd get on the plane and once on the plane throttle adjustments would be immediate. I.e a change in throttle resulted in a change of speed...  However, if I pushed the throttle to WOT when sitting bogged down at those revs the rpm would increase for absolutely no change in speed, or at times a decrease in speed... Andl I could 'feel' as if something was slipping, hard to explain but I knew the increased rpm had caused an issue...

was like this all day, only getting on the plane with the very slightest in rpm increases, if I pushed even the slightest bit harder it would just stay bogged down.

The ultimate goal is to keep an eye out for modernish second hand 60 four stroke but until then I've marked the hub and prop to check for slipping. 

It may sound like I'm clutching at straws but I know it has performed a lot better in the past. 

Cheers

Steve

 So i thought i'd update this.

I decided to check the ignition coil and spark plug lead resistance today and found that one of the four cylinders has a spark plug lead which is open circuit. Threw on a spark tester and it is still getting spark to the plug but can only guess that it's breaking down or failing under load.

Luckily it looks as though the corresponding coil is still good so i'm hoping that replacing the lead will resolve the issue.

I'll update once i've manage to replace the lead and take the boat out.... whenever that may be....

Cheers

Steve 

Issue sorted!...

Was the dodgy spark plug lead...

Cheers 

Steve