very high propeller slip for a 14.83ft/30hp

[Olympic450]

Dear all,
I am an owner of a 14.83 ft fibreglass boat with a Honda BF30 engine. You can see my boat's type and hull here
Manufacturer page
My boat during setup
my boat at the launch

The engine has a 9.25? X 12? propeller. The proposed hp by the boat manufacturer is 20-40hp so I don?t think that my bf30 is underpower for this boat. The console is installed close to the stern so I think that might have the most weight at the back of the boat even if all of the equipment is to the front except the fuel which is at the back and the battery under the console. With this setup I have the following performance numbers with approximately 1200lb total weight (boat [660lb], engine & fuel [220lb],1 person [220lb], boat equipment [100lb]).

RPM speed (knots) slip
1000 2.6 45.2%
1500 3.5 50.9%
2000 4.2 55.8%
2500 4.9 58.7%
3000 5.4 62.1%
3500 6.1 63.3%
4000 8.6 54.7%
4500 12.5 41.5%
5000 17 28.4%
5500 19 27.2%
6000 21 26.3%

Based on the information I read at the internet and the ?feeling? that this setup gives to me during the sailing, is that I have a huge problem. Actually 2 problems, the first is the high end speed which I was expecting approximately 25 knots and secondly the extremely high slip rates especially in the mid rpm range. So I do this post in order to propose me any solution that will improve the above numbers based on your experience and expertise. What do you think the problem is? Someone proposed to have a 4-blade propeller but in what size? Other told me to go to 3 blade again but 11? pitch. Someone else proposed to raise the mounting height. What do you think? I can raise the engine 1 inch if necessary. I can buy a 4-blade if necessary. Unfortunately I don?t have the ability to test different propellers, because I live in a small place and probably I will buy it through the net. Please any help will be much appreciated. I am very disappointed with this setup. Sorry for my English.

Thank you in advance!

 

[dan02gt]

Re: very high propeller slip for a 14.83ft/30hp

What height is your motor currently mounted on the transom? You can reference this by the relation of the anti-cavition plate to the lowest part of your keel or how far the the center of the prop shaft is below it. Everything must be level when you measure this and there are a ton of online guides to help you with this.

That being said high slip numbers are generally a sign of the motor being mounted too high. Do you have any room to take it down a notch or two? It looks like it's all the way down from your video though. I'm assuming your prop is in good shape since the boat is new.

I would ask the dealer about the poor performance before I spent to much time on it.

Also I have to ask this question. You are trimming the motor up after you get on plane right? Because from the video your boat seems to run very flat with no bow lift.

 

[Olympic450]

Re: very high propeller slip for a 14.83ft/30hp

Hi Dan and thanks for your response. My dealer told me that the AC plate is leveled with the bottom (i will check it also). As you correctly notice, engine can not go lower. It can go one "hole" up and that it is what the dealer will try next days. At the same time he will check an 11" pitch propeller. My dealer is aware of the problems and is checking it but as far as i have understood he has no experience in this specific model (it is the first he sells as a redealer). That' s why i spent some effort in order to learn some things and find a better alternative setup.
Yes i trim the boat during plane. During the launch we were two on board and me the heavier was sitting at the bow. The measurements above were taken with me only on board.

 

[dan02gt]

Re: very high propeller slip for a 14.83ft/30hp

Olympic450, you could call Olympic and see what they recommend. Putting your numbers into the trusty Mercury prop calculator it recommends a 9.3"x11" 4 blade Spitfire for the prop.

 

[steelespike]

Re: very high propeller slip for a 14.83ft/30hp

Is your speed by gps?
The first thing I noticed in the videos I found was these boats run with a lot of surface in the water, it could raise slip and lower speed.
I assume this might be to improve the ride in open water.I also notice it turns very flat almost to the point of sliding.
It appears to have a medium V bottom.Does it have an unusual bottom shape.If you trim up does the bow get up higher?
Does the boat have trim tabs? Have you tried it with the tabs released.
The Spitfire prop may help slip Don't know if they make for a Honda.
I looked up some 30 hp motors on setups 1100 to 1200lbs not Hondas but same weight and hp.
Carolina Skiff 28.3,12" prop 2.15 gear ratio 5800 rpm,Dragon fly 13" prop 5975-30.2 2.15 ratio.
Starcraft Pro Camp 12" 5800 27.6 2.15 ratio
I'm sure the Skiff and Dragonfly were faster hulls without a doubt. The Starcraft a little slower.
Watching your hull I don't see those kinds of speeds but yours will surely ride a lot nicer than any of them and handle better. You might give the turning point Rascal a look.

 

[jestor68]

Re: very high propeller slip for a 14.83ft/30hp

First choice would be a Solas(Honda) Saturn(SS) 10 X 11 pitch. More blade area and more cup; a more efficient prop. Putting an 11 pitch aluminum prop on there would only over speed the motor.

You will get more bow rise(and speed) with the Saturn prop due to being able to trim out more.

You could also use a Solas(Honda) Saturn SS 12 pitch. Expect to drop about 200 rpm at WOT with a decent boost in performance. Raising the motor one hole would gain back the rpm otherwise lost and provide even more performance. That one would gain the most performance with a light load, whereas the 11 pitch would be better able to handle a heavier load.

Solas also has an 11 pitch 4 blade Amita prop that would reduce those slip numbers and provide more efficient cruising performance, but less top speed.

Solas makes props for Honda.

 

[Olympic450]

Re: very high propeller slip for a 14.83ft/30hp

@Dan
Yes we will contact the manufacturer at the same time to check with his trial setups

@steelespike
Yes speed measured by gps. The video show the first launch ride (2 pax & 20litres of fuel, nothing else). The measurements have been contacted only with me on board after some months. At the higher speeds >4500 rpm for sure the boat i thinκ is in good plane with only 1/3 on water. Yes the trim up raises the bow. Yes it seems medium V. I dont know what you mean unusual bottom but you can see it at the video called "My boat during setup" at first post to check. I dont have tabs. From the boats you mention i think that the starcraft setup is close to me even if it seems a little bit less weight and also different material (aluminum vs fibre). I found the test you saw also with the envinrude. Be aware that speeds at your tests are in miles/hour (1609m/hour) while my speeds are in knots (1852m/hour). I write down again my performance numbers since you use different metric system for a better perception of the situation. I also write the slip of the above test you mention for comparison and better review of my situation.

RPM	speed (miles/hour)	slip	|	speed (envinrude)	slip (envinrude)
1000	2.99	45.2%	|	2.4	55%
1500	4.03	50.9%	|	3.8	52%
2000	4.83	55.8%	|	5.1	52%
2500	5.64	58.7%	|	6.1	54%
3000	6.21	62.1%	|	6.9	56%
3500	7.02	63.3%	|	9	51%
4000	9.9	54.7%	|	13.9	34%
4500	14.38	41.5%	|	19.3	19%
5000	19.56	28.4%	|	22.9	13%
5500	21.86	27.2%	|	25.5	12%
6000	24.17	26.3%	|	27.6	10% (5800)

You can see that starcraft/envinrude has much better slip rates especially after 4500 which is <20% (proposed for this type of boating according to various sources on the net). This is what i want! A little higher speed after 4000RPM with lower slip rates

@ jestor & steelspike

Going from aluminum to SS in a 30 HP motor? Is it that too much for this kind of boat/engine? From what i have read to the net they propose SS for bigger boats and especially engines. Let me say that i use the boat for fishing so my use is to make 6-7 miles per use to go to the fishing place and back home. I may start trolling in the future. I mean i dont want so much to go to 30 miles/hour high end speed but to make an easier, quicker efficient planing and cruising especially if 1-2 more persons come onboard. With this setup and 3 persons onboard i barely could plane. One of the dealers told about SOLAS AMITA 4 blade but if i buy this should i go to 11" or 12" pitch? Yes the other alternative would be the 4 blade spitfire by mercury which is fine for honda

Thanks again to all of you for this discussion.

 

[steelespike]

Re: very high propeller slip for a 14.83ft/30hp

I know you were using knots I converted to miles per hour
For comparison. I noted that all the boats I checked planed by 4000 rpm allmost as fast speed as yours at 4500.
and of course the slip was lower.
Any of the props suggested by jester should help your performance.
It should be easy to improve on your really high slip numbers.
Solas props have a good reputation for predictable performance.
The Solas Amita 11" Aluminum 4 blade should improve performance close to the stainless prop for about half the cost.
Typically you would drop one inch of pitch when going to a 4 blade.
A stainless prop should offer the best improvement but it could range from a few tenths to a few mph compared to a good aluminum prop. Jerstor knows his stuff about props.
I don't think your hull will produce exceptional speeds but a different prop may improve hull lift beside reducing slip.

 

[Olympic450]

Re: very high propeller slip for a 14.83ft/30hp

Hi all,
Here is an update on my situation. The last 3 months the boat was out for winter, the engine raised one hole and now the AV plate is almost even with the bottom of the hull and 1/4 of the inch above. The hull is clean and the tests were contacted with 2 persons on board (240lb close to the stern and 165lb at front), i.e. total weight including boat, engine, gas, battery and 2 pax 1320lb. Wind blow 8-10 km/h with small wavelets. We tested 2 props, my old one (9.25 X 12) and a prop that i borrow for the test (9.9 X 10). The results are:

RPM	m/h (10'')	slip (10'')	m/h (12'')	slip (12'')
1000	2.4	47%	2.1	62%
2000	4.8	47%	4.9	55%
2500	---	---	5.7	58%
3000	---	---	6.7	59%
3500	---	---	7.6	60%
4000	---	---	9.6	56%
4500	11.2	45%	14.1	43%
5000	16.4	28%	18.1	34%
5500	19.4	23%	21.3	29%
WOT	6200 / 24	15%	5800 / 23.5	26%

I didn't took measurements for mid range RPMs for the 10''. I noticed the below:
1) Raising 1 hole (approximately 1'' the engine) performance was not influenced comparing my old measurement with yesterdays for the 12''
2) The 10'' show better slip rates but speeds at mid range is again out of the question.
3)10'' slightly better WOT speed but close to over rev.

Based on the above what do you suggest? How the problematic situation can be fixed, if it can?
Thanks in advance.

 

[steelespike]

Re: very high propeller slip for a 14.83ft/30hp

In my mind the 450 runs very flat with a lot of surface in the water this drag no doubt increases your slip numbers.
I also think that the reverse chine in contact with the water all the time increasers drag.
There must be other 450s in your area you could compare to.
The Starcraft test you mention above is a poor comparison. The Starcraft doesn't have a reverse chine like your boat
And it very likely runs with only 1/4 to 1/3 of the boat in the water at speed.
I can't be specific but a prop with good bow lift may help ,and I think its obvious that an 11" is closer to what you need.
It is unusual to go to a smaller prop and gain speed.I think the increase comes from the close to normal slip.
I think if you watch the 450 video you will note the way the boat seems to lay down also I don't see any reference to speed other than the the phrase "satisfactory performance" I haven't seen any hard speed numbers from the videos.
In my opinion the hull isn't designed for speed but for handling and smooth dry ride.
If you haven't had any venting with the new motor height you may be able to raise it another hole.
I think I would get an 11" prop first and run it before raising the motor more.
I don't think you will come close to the speed of the Starcraft in the test.

 

[Olympic450]

Re: very high propeller slip for a 14.83ft/30hp

Hi steelspike and thanks for your answer. OK so i understand that i can not achieve better WOT speeds and that will be acceptable. I will try to find another 450 in the area (i know someone who has it with a yamaha F30 (747cc)). However, based on that measurements is there any way that i may raise my speed after 4000rpm? As far as i understood a 4blade may raise it but based on your last post my bow should raised and a 4blade will have the opposite result, i.e. raise the stern. Unfortunately i can not raise the engine more unless i make new holes and i want to avoid that.
Some questions:
Raising the engine what is the effect to the bow?
What are the possible alum props that would raise the bow?
Installing more gear/weight close to stern will help the situation?
Do you think that according to these results i may have sick engine? (carburetor synchro, timing, compression? etc)
Thanks again

 

[steelespike]

Re: very high propeller slip for a 14.83ft/30hp

I think the Solas (Honda)Saturn 10 X 11" suggested by Jestor68 Would be ideal.
As he said More blade area,more cup,more efficient design.
He has a good reputation for prop selection.He understands better than I the subtleties of prop design
and what the results would be.
Raising your motor Probably won't affect the bow but the less you drag through the water the better.
I would get the saturn prop and do some tests before any other alterations.If you have no venting trouble
you probably could raise the motor one hole.Usually it is suggested that the anti vent plate be barely visable at speed.
One Al. prop that could raise the bow is the Turning Point Hustler or Rascal. I haven't checked their site recently
They have made some changes with their replaceable hub and possibly their prop names.
They have a reputation as aggressive al props that deliver close to ss performance.
Moving weight to the stern could help.
I think your motor is healthy. The 12" prop produces 5800 rpm And there are only 2 sizes bigger.
So your propped slightly to the high side of the chart with a good result other than the high slip.
You certainly wouldn't call your boat light like a bare 15 ft aluminum boat.